Calibration of Shallow Borehole Drilling Sites Using the Electrical Resistivity Imaging Technique in the Granitoids of Central Region,Ghana

The electrical resistivity imaging (ERI) technique has been used to calibrate existing successful and dry borehole drilling locations in the Cape Coast Granitoid Complex of the Central Region of Ghana. The area has a low groundwater potential and most of the communities do not have access to potable water. Surface water is generally expensive to treat and is therefore not considered as a good water supply option in such rural and dispersed communities where incomes are low. Supply of water to communities from existing boreholes is inadequate. Therefore, there was the need to construct more boreholes to increase access to potable water to meet coverage targets. Results show that the ERI technique is capable of detecting shallow bowl-shaped conductive zones up to 75 m represented by low resistivity values mainly due to weathered granitoids and/or fractures within the granitoids. Resistivity values typically less than 500 Ω-m obtained between depths of 10–50 m on model resistivity sections accounted for about 80% of successful productive boreholes. Resistivity values in the range 500–1,500 Ω-m represented marginally successful borehole locations which could be suitable for hand-pump installation and values greater than 1,500 Ω-m were confirmation for dry borehole locations.