Assessment of Aquifer Vulnerability Using Geoelectrical Parameters in Delta State

This study assesses shallow aquifer vulnerability to contamination using geoelectrical parameters derived from vertical electrical soundings in parts of Delta State, South South Nigeria. Aquifer vulnerability assessment is critical in Delta State, where prolific oil and gas production, agricultural chemical use, and unregulated waste disposal create multiple contamination threats to shallow groundwater that is widely used for domestic supply. Geoelectrical methods provide spatially distributed hydrogeological parameters needed to compute aquifer vulnerability indices. This study acquires Schlumberger VES data at 30 stations in Ughelli North, Ethiope East, and Okpe local government areas with maximum AB/2 of 200 metres. Layer models are extracted from IX1D inversion and used to compute protective cover, longitudinal conductance, and transverse resistance as vulnerability indices following the DRASTIC and hydraulic approach methods. Dar-Zarrouk parameters are mapped spatially across the study area. Selected water samples from shallow wells and boreholes are analysed for nitrate, iron, and total coliform bacteria to validate the geophysical vulnerability predictions. Findings reveal that 62 percent of the study area is characterised by high to very high aquifer vulnerability, corresponding to areas with thin or absent clay protective layers below 3 metres thickness and longitudinal conductance below 0.15 siemens. Water quality data confirm elevated nitrate and bacterial contamination in wells from high-vulnerability zones, providing geophysical validation. Areas of very high vulnerability coincide with agricultural zones receiving heavy fertiliser application. The study produces a vulnerability zonation map for integration into Delta State groundwater management planning.

Keywords: aquifer vulnerability, geoelectrical parameters, Dar-Zarrouk, Delta State, contamination risk.