Assessment of groundwater quality and soil properties in recharge and discharge areas of a basement environment

This study examined the interaction between soil and groundwater in a recharge and discharge areas of Akungba-Akoko, Southwestern Nigeria. Ten water samples (R1–R5 from the recharge and D6–D10 from the discharge areas) and ten soil samples from trial pits were collected and analyzed for hydrochemical parameters (Ca2+, Mg2+, K+, Na+, Cl+, SO42+, NO3−, PO43−, Fe, Zn, and Pb) and geotechnical investigation. Ten Schlumberger vertical electrical sounding (VES) were carried out to determine the subsurface resistivity distribution. The concentrations of all the hydrochemical parameters including Ca2+ (0.06–0115 mg/L), Mg2+ (0.05–0.099 mg/L), K+ (0.021–0.042 mg/L), Cl− (3.778–9.885 mg/L), Zn (0.01–0.025 mg/L), and Pb (0.003–0.004 mg/L) were within the WHO stipulated standards. Geotechnical tests revealed that the soil was sandy-clay loam with a subgrade rating of A-2–6 or A-2–7 and medium compressibility, indicating the soil was suitable for agricultural purposes. Grain size analysis showed that the sand content of the soil (average = 48.2%) is ideal for agriculture. The VES model revealed four lithologic layers with four curve types (HA, AA, AK, and HK). The wells were located in clayey to sandy-rich weathered layer (66.9–794.4 Ωm) with an average thickness of 11.4 m. The thin layer was responsible for the observed variations in groundwater during the dry season. Two viable fracture zones were identified with good potential. The health risk assessment, drinking water, and irrigation indices (WQI, SAR, SSP, KR, and MH) indicated that the groundwater in both areas was good for drinking and irrigation purposes, with no associated health risks. Nine pairwise parameters were identified with a strong correlation between changes in groundwater quality (sodium content) and the resistivity response of the soil. Continued monitoring of groundwater quality and soil resistivity response will provide effective groundwater management strategies.