Application of Second-Order Geo-electric parameters in the Determination of Groundwater vulnerability in Sedimentary Terrain, Iyowa, Edo State Southwestern. Nigeria

Abstract

The application of vertical electric sounding (VES) techniques to evaluate groundwater vulnerability and groundwater potential was carried out in Iyowa, Benin city, Southern part of Nigeria. Five (5) VES points randomly selected in Schlumberger configuration was deployed for the VES with a view to investigate, access and classify areas most vulnerable to contamination. The Petrozenith Terrameter was used with maximum spread of 800m (AB/2=400). The INTERPEX 1D software was used for the data iterations. The study revealed the presence of four curve types which includes: 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 (ρ_L), transverse resistivity (????_t) and formation anisotropy (λ). The survey was conducted using vertical electrical sounding (VES), employing Schlumberger electrode configuration. 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 (ρ_L), 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. thus, the average aquifer protection capacity rating was considered 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. 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 imply 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 anisotropic value revealed that the study area’s aquifer generally has good porosity and permeability.