Assessment of groundwater potential and quality using geophysical and physicochemical methods in the basement terrain of Southwestern, Nigeria

Abstract

An integrated approach involving geophysical and physicochemical methods was undertaken to assess the potential availability of groundwater and its quality was carried out at Akole, Abeokuta Southwestern Nigeria. A combination of electrical resistivity and natural electric field methods were used in delineating the sub-surface lithology, determining potential groundwater-bearing zones, and the potential availability of groundwater for a community water supply. Laboratory analyses of samples from existing wells in the area was also carried out to determine the groundwater quality index (GWQI). Four vertical electrical sounding (VES) stations and nine profiles were surveyed using the Omega Campus and PQWT 150 instruments, respectively. The VES results delineated a maximum of five geo-electric sub-surface layers. A sudden change in the stratigraphy view of the rock formation from soft to very hard formation was observed in profile map L2. Profile map L7 and VES 2 has the highest potential for future groundwater exploration. Areas under VES 3 and profile maps L2, L3, L4, L5, L6, L8 and L9 are categorized as having a “medium” groundwater potential while the low yield water potential are areas under VES 1 and 4 and, profiles maps L1 and L10. The majority of groundwater in the weathered/fractured aquifer of the study area is slightly acidic. The GWQI values were less than 100, an indication that the analysed water samples fall within the “excellent” and “good” quality categories, implying that the groundwater is fit for domestic purposes. A combination of geophysical and physicochemical techniques has been successfully used to provide useful information for the assessment of groundwater potential and quality of the community.