ABSTRACT
Groundwater vulnerability assessment was carried out at Iguekhinkhwin, Iyowa, Benin city, Southern part of Nigeria, with a view to investigate, access and classify areas most vulnerable to contamination. The survey was conducted using vertical electrical sounding (VES), employing Schlumberger electrode configuration. Five (5) VES points were selected. The Petrozenith Terrameter was used to record resistivity readings and sound curves were created with the use of WINRESIST software, which facilitated data processing. The study revealed the presence of four curve types. Namely: HAK (40%), HAQ (20%), AKQ (20%), and AAK (20%) respectively. The second-order geo-electric parameters interpreted were longitudinal conductance (S), transverse resistance (Tr), longitudinal resistivity (ρL), transverse resistivity (t) and formation anisotropy (λ). The values of longitudinal conductance in the study area ranged from 0.13 Ωm to 0.52 Ωm with an average of 0.24 Ωm. According to the aquifer protection rating capacity, VES 1 and VES 4 are moderate, while VES 2, VES 3 and VES 5 are weak. However, the average aquifer protection rating capacity in the study area is moderate. Tr values ranged from 304038.7 Ωm2 to 1058541.0 Ωm2 with an average of 1019307.76 Ωm2, which indicated that the study area has very high transmissive capacity of regional importance. Longitudinal resistivity of the study area ranged from 373.369Ω-m to 1276.027Ω-m, with an average of 2004.681Ω-m. The longitudinal resistivity value reveals the lithologic unit in VES 3 to be Lateritic-sand, while VES 1, VES 2, VES 4 and VES 5 are inferred to be laterite. Transverse resistivity values in the study area ranged from 3755.42 to 1743.662 with an average of 5413.11. The high transverse resistivity values across all VES points implies the existence of impermeable layers like bedrock or clay in the study area. Anisotropy values ranged from 2.627 to 1.244, with an average of 1.83. The low anisotropic value revealed that the study area’s aquifer generally has good porosity and permeability. The study area generally has low aquifer vulnerability to contaminants.
