Locating Aquifers in Crystalline Granitic Rock Using Electrical Resistivity Technique in the Sissala East District of Ghana

Groundwater prospecting in the Sissala East District has been conducted using the electrical resistivity method.  This has been done with the objective of locating suitable sites for borehole drilling and to determine groundwater potential of the district. The dipole-dipole technique of the electrical resistivity method was conducted using the McOhm 2119 resistivity meter in the horizontal profiling (HP) and vertical electrical sounding (VES) modes simultaneously. Geophysical data taken in both the HP and VES modes were presented in two dimensional (2-D) coloured vertical cross sections, from which VES curves were also plotted for selected station points and interpreted qualitatively. Results of the 2-D vertical cross sections and VES curves predicted an average depth range of groundwater or moisture interception of 10 to 15 m. The apparent resistivity of the wet boreholes was in the range of 15 Ωm and 300 Ωm. These were quantitatively confirmed with drill logs of the wet boreholes. The drill logs further showed that main aquifers and fractures were encountered between 20 m and 50 m depth range. The results yielded a success rate of about 89 %, thereby indicating that the district has a great potential for groundwater to meet their domestic and irrigation needs. Therefore, the dipole-dipole technique is effective in locating aquifers for groundwater in crystalline granitic rocks. Keywords: Groundwater, Crystalline granitic rock, Aquifers, Apparent Resistivit

Electrical Resistivity And Induced Polarization Imaging For Refuse Dump Site

Contamination from landfills as a result of leaching from organic and inorganic waste poses a threat to the environment because, subsoil and groundwater are affected. The contamination is more serious in developing countries where waste management is inefficient. The aim of this study was to determine the extent of pollution at this site. Three profiles were surveyed: two in North-South direction and the third in Northeast-Southwest. 2D electrical resistivity and Time Domain Induced Polarization (TDIP) data sets have been acquired along the three profiles in Boadi Community. Electrical resistivity and induced polarization together with excavations were successful in mapping the extent of the leachate plume. The study demarcated clearly three main zones: the first, second and third zones indicated chargeabilities > 12.8 msec near the surface, > 6.4 msec and > 12.8 msec at the base respectively. Similarly, resistivities < 12 Ωm, 12 to 24 Ωm and >192 Ωm for the first, second and third zones respectively were delineated. The relatively lower electrical resistivity areas were thought to be due to the presence of the leachate plume and the comparatively higher chargeability zones were interpreted as duricrust. The relatively lower chargeability represents absence of polarizable materials. The study also delineated the weathered basement granodiorites showing relatively higher resistivities. These TDIP and ERT results show that the methods have been successful in mapping the landfill leachate plume. The results from the resistivity and chargeability compare very well with the excavations

Electromagnetic Method and Vertical Electrical Sounding for Groundwater Potential Assessment of Kintampo North Municipality of Ghana

Electromagnetic (EM) profiling and Vertical Electrical Sounding (VES) of electrical resistivity method have been employed to explore for groundwater in the Kintampo-North Municipality in the Brong Ahafo Region of Ghana. The EM profiling data were obtained with GEONICS EM 34-3 equipment at 20 m intervals along 20 profiles of length ranging between 70 to 240 m to determine conductive anomalous zones for further investigation within the unconsolidated overburden and/or water-bearing fissures in the bedrock. Subsequently, using the ABEM Terrameter, VES employing the Schlumberger electrode configuration was carried out at previously selected 53 promising anomalous points on the EM profiles. The modelled VES data using RES1DINV software revealed a number of subsurface layers and their corresponding apparent resistivity values and thicknesses. The results indicated that the EM terrain conductivity anomaly in the study area varied in the range 6-87 m mhos/m with the average and maximum apparent conductivity values of 48.5 and 76 m mhos/m respectively. The VES revealed three to four-layered lithological subsurface sequence, indicating decreasing apparent resistivity with depth. This depicted the general trend of ρ1< ρ2>> ρ3≤ ρ4, where ρ1, ρ2, ρ3 and ρ4 are the apparent resistivity of the layers 1, 2, 3 and 4 respectively. The results further showed that both the average apparent resistivity and thickness of layers 1, 2, 3 and 4 are respectively 368 Ωm, 3.9 m; 435 Ωm, 17 m; 50 Ωm, 53.5 m and 332 Ωm, >53.5 m. Thus aquifer zones were estimated to be located between 15-30 m depth. These layers were inferred to be the sandy-clay topsoil, weathered/fractured layer and the fresh bedrock. However, the weathered layer and the fractured basement constituted the aquifer zones across the study area within the Voltaian Sedimentary Basin, which is otherwise regarded as a difficult area in locating groundwater resources. Keywords: Groundwater potential, aquifer, apparent resistivity, terrain conductivit

Prospecting for Groundwater Using the Continuous Vertical Electrical Sounding Method

2-D CVES surveys using the Wenner configuration was carried out in 22 communities in the Tain District, Ghana. This was done with the objectives of assessing the subsurface geology, identify high groundwater potential zones for drilling high-yielding boreholes that could yield sustainable amount of groundwater. The collected resistivity data were converted from the apparent resistivity to 2-D modelsection using the least-square inversion algorithm with the help of Res2DInv software. The 2-D resistivity model-sections produced a high quality structural resolution leading to the demarcation of the layering of various lithological units, weathered layers and identification of important structures such as joints, fractures and faults. Quantitatively, it can be observed that all the drilled wet wells have aquifer zones between 30 m and 60 m within sandstone, siltstone and phyllite granitic environments. The result of the borehole drill logs revealed that the aquifers were within weathered and fractured zones and is in agreement with the models. The results showed that the boreholes yield within the study area varied between a minimum of 15 litres/min to a maximum 800 litres/min and the mean depth for intercepting aquifer was at about 30 m and below. The study revealed that the potential aquifer zones in the study area are mostly as a result of weathering of the overburden and fracturing of the underlying bedrock. The results suggest that the hydrogeology of the study area is highly complex since the development of groundwater is generally due to secondary porosities