Abstract:
The major source of potable water in Tarkwa is the Bonsa Treatment Plant sourced from the Bonsa River. The activities of
illegal miners along the banks of the Bonsa River has resulted in pollution of the river. This has resulted in high treatment
cost and irregular supply of water to the Tarkwa Township and surrounding communities that are fed by the Bonsa
Treatment Plant. In view of the difficulty in getting frequent and regular potable supply of water, people have resorted to
construction of boreholes and hand-dug wells. However, the success rates and borehole yields are low especially in the
hydrogeologically difficult terrains in the Tarkwa area. The aim of this paper is to investigate the hydrogeological conditions
of the Tarkwa area using both the Electrical Resistivity Imaging (ERI) and Electromagnetic (EM) geophysical techniques to
determine the electrical resistivity and conductivity values that are related to groundwater accumulation, so that potential
water-bearing zones can be identified. Results from electrical resistivity show that the general resistivity distribution in the
Tarkwa area is between 32 Ωm and 100 000 Ωm. Water-bearing zones in the Huni Sandstone occur to a depth of 35 m with
an average resistivity value of 400 Ωm, at a depth of 60 m and a resistivity of 600 Ωm in the Tarkwa Phyllite, at a depth of
55 m and a resistivity of 600 Ωm in the Banket Series and 50 m depth with resistivity value of 500 Ωm in the Kawere
Conglomerate respectively. The electromagnetic conductivity values also show that the general conductivity distribution in
the Tarkwa area is 3 – 32 S/m. The application of electrical resistivity and electromagnetic techniques separately gives
success rate of 80 % and 65 % respectively. An improved success rate of 86 % is achieved combining the two techniques.
