Geo-electrical and physicochemical appraisal of aquifer potential and protective capacity in Ketu-Alapere, Lagos, Nigeria

Abstract

Aquifer potential with emphasis on groundwater quality by delineating subsurface lithology, identifying groundwater-bearing zones, assessing aquifer protective capacity, and analyzing water quality was appraised in this study. An integrated approach combining geophysical and physicochemical methods was adopted, including Vertical Electrical Sounding (VES), Constant Separation Traversing (CST), and laboratory water analysis. Seventeen VES stations and five CST profiles, each approximately 200 m long, were acquired. Geophysical data were interpreted using partial curve matching and iterative computer modeling. Groundwater samples from a well and a borehole were analyzed in accordance with ASTM and APHA standards. The results indicate four to five geo-electric layers comprising topsoil, clay, sandy clay, clayey sand, and sand (aquifer). The aquifer occurs predominantly within the fourth geo-electric layer at most VES locations (VES 6, 10, 11, 12, 14, 15, 16, and 17), except at VES 6, where it appears in the fifth layer. Aquifer resistivity values range from 101.3 to 433.1 Ωm. Longitudinal conductance values suggest moderate to good aquifer protective capacity. CST 2D inversion corroborates the lithological interpretations from VES. Physicochemical results show acceptable total dissolved solids and major ion concentrations; however, slightly acidic pH and elevated chemical oxygen demand in the well sample exceed WHO limits, indicating the need for water treatment before domestic use.