ABSTRACT
ABSTRACT: The Keta Basin forms one of the five coastal sedimentary basins in the southern part of the country. The top sand-plain is an extensive shallow aquifer used for both the domestic and agricultural water supply. Very recently, a number of shallow boreholes were drilled into the shallow freshwater lenses and fitted with submersible pumps. Studies conducted on the water quality suggest an increase in the chloride content of the aquifers and the possibility of salt-water intrusion into this aquifer. The paper deals with the application of electrical resistivity techniques to delineate formations bearing fresh and saline water, distinguish between sandy and clay layers and establish the depth to the freshwater-saline water interface. Results of the VES conducted for test wells AN1, AN2 and AN3 indicate that the northern sector is basically underlain by a four-layer structure. The top layer has an average apparent resistivity of 27.1 Ohm-m and an average thickness of 6 m. The infinitely thick bottom layer has an apparent resistivity of 0.2 Ohm-m, which was confirmed to be due to an extremely thick layer of clay, probably saline water-saturated. An analysis of the geophysical data also indicates that the freshwater-saline water interface in the Anloga area lies at an approximate depth of 40 m, close to the shoreline to a maximum depth of about 100 m at the midportion between the lagoon and the sea. Test drilling close to the lagoon has also confirmed that the interface lies beyond 14 m in the vicinity of the lagoon.
