Physical Science International Journal

Aims: This study assessed the use of geophysical methods in investigating aquifer properties and vulnerability

Place and Duration of Study: Eti-Osa and its surroundings, Lagos, Southwestern Nigeria; between 2023-2024.

Methodology: This study combined electro-geophysical and hydrogeological techniques to investigate aquifer geo-hydraulic parameters. Electrical resistivity was measured using the ABEM SAS 4000 resistivity meter in the Schlumberger configuration, with a maximum current electrode separation of 1000m. Thirteen VES datasets were acquired along profiles and analyzed to produce a layered earth model. Computer-iterative inversion models simulated the VES data, generating resistivity curves for interpretation of the subsurface geo-electrical structure.

Results: Results of the study show that the highest aquifer resistivity recorded within the study area is 961Ωm while the least is 11.7Ωm with a mean resistivity of 289.5Ωm. Aquifer thickness ranged from 25.3m to 11.68m, and aquifer depth varied between 41.5m and 15.23m. Longitudinal conductance of the aquifer across the study area varied from 1.504Ω⁻¹ to 0.015Ω⁻¹ while aquifer transverse resistance ranged from 13564.8Ωm² to 205.92Ωm². Results of aquifer hydraulic parameters show that hydraulic conductivity across the study location varied between 0.6666m/day and 0.1940m/day with aquifer transmissivity varying between 14.94m²/day and 2.8m²/day. Aquifer storativity ranged from 0.000035/m to 0.0000759/m, while hydraulic diffusivity varied between 373403.2m² /day and 87687.44m²/day. In addition, a novel model equation for accurately predicting longitudinal conductance from aquifer resistivity for the study area and regions with similar geology was generated and validated using statistical parameters. Results of aquifer vulnerability showed that 69.23% of the total sampled area is strongly susceptible to surface pollutants, 23.01% showed moderate susceptibility, and 7.69% possess good aquifer protective capacity.

Conclusion: This study has revealed that measures should be put in place in this area to protect groundwater resources and guarantee their availability for future generations. Effective groundwater management including stakeholder participation, continuous monitoring, and the integration of geophysical methods with other hydrogeological studies is, therefore, recommended.