Geophysical investigation of groundwater potential and aquifer protective capability in selected communities within Cape Coast municipality, Ghana

Abstract

AbstractApplication of VES geophysical technique to investigate the groundwater potential and the aquifer protective capability has been carried at Cape Coast Municipality, Ghana. The geology of Cape Coast is mainly made of the Secondian formation and the Eburnean Plutonic Suite. Twenty (20) VES points were selected after the profiling, and Schlumberger array was applied for the conduction of the VES. The PASI Resistivity Terrameter was used, and the maximum current electrode spacing (AB/2) was 100 m. Partial curve matching technique and computer iteration technique were applied in the interpretation data using WINRESIST software. The thematic maps of the parameters were generated to display their spatial variations using Surfer Golden software by the application of appropriate variograms depending on their range of values. The study revealed the presence of three to six layers curve types which include HKH (45%), QH (20%), HA (10%), KH (5%), QHKH (5%), A (5%), AKH (5%) and KHKH (5%) in the study area. The layers include topsoil (31.00–9135.00 Ω m), weathered layer (2.35–60,801.00 Ω m), fractured basement (4.39–32,431.00 Ω m), and fresh basement (59.40–22,521.00 Ω m). About 70% of the resistivities are less than 600 Ω m indicating the possibility of a fractured formation with high potential groundwater storage. The other 30% recorded high bedrock resistivities values of possible massive crystalline granitic rock with a limited fracture. Reflection coefficient and longitudinal conductance were calculated using appropriate equations and parameters. The values of the reflection coefficient ranged from 0.215606 to 0.997049. The study revealed that 20% of the total VES points have high groundwater potential, 65% showed medium potential, 5% showed low potential, while 10% showed very low potential. The study revealed poor (20%), moderate (35%), good (30%), and very good (15%) protective capacity ratings in the area. The technique has been effective in revealing the groundwater potential and the aquifer protective capability of the area. The aquiferous zone of the Secondian formation falls within the range of 17–43 m of depth with a borehole yield of 210–240 l/m. The successful borehole in the granitic rocks shows a low yield of 10 l/m with a water-saturated zone within 20–48 m of depth.