Groundwater prospecting using the dipole-dipole configuration for vertical electrical sounding: prediction of major aquifer depth in the Tolon-Kumbungu district of Northern Ghana
A geophysical investigation in groundwater prospecting, using the vertical electrical sounding (VES) method in resistivity surveying, was undertaken in the Tolon-Kumbungu district of Northern Ghana. The aim was to evaluate the effectiveness of the VES technique as a low-cost groundwater exploration method. Using the dipole-dipole VES technique, fracture zones that held good prospects for groundwater location were prospectively identified at 15 sites in the Gbullung and Wayamba communities of the district. In addition, retrospective VES data for 6 sites were obtained from previous studies. Geophysical VES data and available drill logs for 3 sites in the prospective study and all 6 sites in the retrospective study (a total of 9 sites) were then evaluated by the VES log-log graph interpretation method to establish a correlation with the groundwater characteristics of the study area. The analyses of the VES curves indicated the presence of anomalous fracture zones occurring within hard sandstone formations that had high groundwater potential. Weathered zones or fresh rock aquifers however did not show potential for groundwater. The dominant formations in the area were found to be thin-bedded sequences of sandstone, mudstone, shale, siltstone and their intercalations. Groundwater was confined to between the depths of 25.0 m and 40.0 m, with major aquifers occurring approximately between the depths of 34.0 m and 45.0 m. These predictions were confirmed by the available drill logs. Using the VES curve interpretation as a means of selecting promising water-bearing sites, 8 out of the 9 sites drilled were successful wells, recording water yields ranging from 14 L/min to 250 L/min, with an average yield of 87.3 L/min. The study thus showed that the dipole-dipole VES technique in groundwater prospecting is effective for the geology of the study area.
Keywords: Tolon-Kumbungu; vertical electrical sounding; aquifer; groundwater; apparent resistivity