Appraisal of Groundwater Potential Zones and Quality in the Sedimentary Formation of Southwestern Nigeria Utilizing Geophysical and Hydrochemical Methods

An integrated method including hydro-chemical and geophysical techniques was utilized to assess the potential availability and quality of groundwater in Apaken, a suburb of Sagamu in southwest Nigeria. A combination of natural electric field and electrical resistivity methods were used to define the underlying lithology, which may include groundwater. Twelve vertical electrical sounding (VES) locations and six profiles were surveyed using the Terameter and PQWT equipment, respectively. To ascertain the groundwater quality index (GWQI), laboratory tests of samples from nearby wells were also conducted. A maximum of five geo-electric subsurface layers were identified by the VES data. Profile map L2 showed a sharp shift in the stratigraphic view of the rock formation from a soft to a very hard formation. Groundwater exploration had a very high yield potential for sounding points (VES 6, VES 7, and VES 10) towards the due to a reflection coefficient (RC) of less than 0.8 and an overburden thickness (OT) of more than 13 meters in the southern portion of the research region. In the meanwhile, the yield zones for medium groundwater potential (VES 1 and 9) towards the north and southeast respectively had OT > 13 m and RC > 0.8 while low-and very low yield groundwater potential zones (VES 2-5, VES 8, VES 12), which were located predominantly at the research area's northern section were of OT < 13 m but of RC > 0.8 and RC < 0.8 respectively. Nonetheless, the aquifer protection capacity metrics suggested that roughly 92% of all VES points are rated as "poor," while the remaining 8% reflected weak aquifer protective capacity. According to Piper trilinear analysis, the bulk of groundwater samples are of fresh water status and CaHCO3 type. The GWQI readings were below 100, which suggests that the groundwater is suitable for residential use and places the examined water samples in the "excellent" and "good" quality categories. Effective information for evaluating the region's groundwater potential and quality has been obtained through the effective application of a combination of hydro-chemical and geophysical approaches.