Improving Access to Potable Water Supply using Integrated Geophysical Approach in a Rural Setting of Eastern Ghana

Hydro-geophysical investigations were conducted on a 16-acre piece of land at KaedabiAhwerease in the Akuapem-South Municipality in the Eastern Region of Ghana. The purpose of the study was to determine the groundwater potential at the site and the possibility of drilling a borehole that could yield considerable quantity of groundwater for sustainable potable water for a proposed bottled and sachet water factory. The survey was carried out using the Geonics EM-34 conductivity meter and ABEM Terrameter (model SAS 1000 C) equipment. Electromagnetic (EM) profiling and Vertical electrical sounding (VES) surveys were conducted to determine the vertical variation of the resistivity/conductivity of the sub-surface rock formation with depth with the view to detecting fractures, joints, shear zones and faults, which could serve as conduits for water traps within the underlying bedrock at the project site. The EM profiling data were obtained along three (3) evenly-spaced parallel traverses each of length 300 m with the 20 m inter-coil separation cable. Measurements were taken at 10 m station intervals in the northwest-southeast directions as a means of selecting suitable points for depthprobing (VES investigations). From the EM profiling results, 12 conductivity anomaly points were selected for further investigation using VES methodology. The Schlumberger array was used for the VES survey. The combined interpretation of the EM and VES results indicated the presence of possible aquifer units comprising the weathered, fractured and fresh bedrock within the subsurface of the study area. The results revealed the presence of three geo-electric layers. The resistivity of the top lateritic layer ranged from 78 to 1,895 Ωm with thickness between 0.8 and 1.7 m. The resistivity of the regolith (second layer) ranged from 10 to 135 Ωm with thickness of 2.1 to 6.4 m; while the bedrock had resistivity values between 303 and 1068 Ωm. The combined output from topographic interpretation, paleo-river channel location and resistivity modeling results clearly zoned out areas of high and low groundwater potential in the study area. The estimated groundwater yield for the three test wells drilled within the detected high groundwater potential zone ranged between 50 and 160 litres per minute (lpm), indicating that, the study area has adequate groundwater for the proposed project. © 2016 Elixir All rights reserved. Elixir Environ. & Forestry 95 (2016) 40714-40719 Environment and Forestry Available online at www.elixirpublishers.com (Elixir International Journal) Evans Manu et al./ Elixir Environ. & Forestry 95 (2016) 40714-40719 40715 The application of the electrical resistivity method over the years is highly documented in several scientific papers. It has been used successfully for groundwater exploration in hard rock terrain (Anechana et al. 2015; Nwankwo, 2011; MacDonald et al., 2001; Mohammed et al., 2012; Sharma and Branwal, 2005; Okrah et al., 2012; Darko and Krasny, 2000; McNeill, 1990) and also in sedimentary formations (AlBassam, 2005; and Claudia et al., 2003). It has to be underscored that, it is high cost and time-consuming to conduct vertical electrical sounding in a given location without having prior knowledge of a potential anomaly point. In the light of this, the electromagnetic method has been used over the years to serve as the reconnaissance tool to map out the conductivity contrast between the target and the host rock. It has also been used extensively for hydrogeologic studies including estimation of groundwater volume (Barry et al., 2010), mapping groundwater contaminant (Benson et al., 1997), groundwater exploration in fissured media (Bernard and Vella, 1991) and also in hydro-geophysical studies (Denielsen et al., 2003; Cook et al., 1992). The combined application of both geophysical methods in delineating potential groundwater drilling points for sustainable water supply will give detailed information about the geological and hydrogeological characteristics of the aquifer in terms of their overburden and aquifer thickness, bedrock resistivity, and vertical resistivity variation of the underlying geo-electric layers. This study seeks to delineate possible high groundwater potential points that could yield considerable amount of water supply for the intended bottled water production.