Groundwater exploration in the Fanteakwa District of the Eastern Region of Ghana using the dipole-dipole method

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Electrical Resistivity of the ground was measured in 100 communities in the Fanteakwa district of Eastern Region of Ghana. in research to explore for groundwater for the community. The lateral and vertical variations of the subsurface were determined. ABEM Terrameter SAS 300 C metre was used to execute the lateral (profiling) and vertical (sounding) variation in Dipole-Dipole configuration. The maximum profile line was between 155 m and 275 m. The maximum electrode spacing for the vertical sounding was between 60 m and 90 m. Profiles were carried out, probing the depth of 30 m, 40 m and 50 m and the results were used to locate the lateral variations of the subsurface, which were then further investigated by vertical electrical sounding (VES). The apparent resistivity measured in the communities underlying the Birimian formation were low of less than 500 ohm -m. Extremely high formation resistivities of less than 2000 ohm -m are found in communities underlying the Voltaian formation. The aquifer boundaries appear to be well defined and delineated to locate zones that have groundwater potential. The geoelectrical model seems to be a satisfactory representation of the aquifer system. Hydrogeologically, however the sites selected for drilling was of more interest, because it could confirm the presence of considerable freshwater. In all, 98 boreholes were drilled in the communities and the success ratio was 65%. The upper layer extends to a depth of 1.2 m to 13.0 m and its resistivities vary between 100 ohm -m and 2500 ohm-m. Correlation with the drilling result of the borehole shows that this part is composed of predominantly coarse-grained sediment, and pebbles to sand. Groundwater was struck in the boreholes at depths between 20 m and 50 m that coincided with the depth to the bottom of the weathered zone of the VES model curves where suitable groundwater is normally located. The lowest yield of 11 litres per minute was obtain from borehole number FA-26 VSP4 and the highest of 300 litres per minute from borehole numbers FA- 54 VSP1, FA-61 VSP6 and FA-62 VSP2. The groundwater contour map and flow nets indicated that Longitude between 0o 281 V and P 211 W and Latitude between N 6° 251 and N 6o 341 locations are recommended for favourable sites for new wells, as it is in an area of high permeability values and where flow lines converge.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the Degree of M.Sc. (Geophysics) , 2000