Assessment of Aquifer Vulnerability and Groundwater Prospects Using Electrical Resistivity Method in Parts of Nnewi Southeastern Nigeria

Abstract

The assessment of the aquifer vulnerability and groundwater potential of Umudim, Okpunoeze, Umudimkwa and Okpunoegbu all in Nnewi town of Anambra state southeastern Nigeria was carried out. An electrical resistivity survey using vertical electrical sounding (VES) employing a Schlumberger electrode array was conducted in fifteen locations (A-0). Also, the data generated was used to interpret the aquifer thickness which ranged from 23.12-108.83m and the depth to the water table ranged from 25.41-99.42m. Additionally, the aquifer properties such as hydraulic conductivity (0.1227 to 3.0931m/day) and transmissivity (3.9139 to 79.3152m2/day) and the Dar-Zarrouk parameters longitudinal conductance (0.00107 to 0.0246Ωm) and transverse resistance (3.6 x 103 to 2.3 x 105Ωm2) were obtained. The VES curves identified were mostly K with some A and H types. At least five to six geoelectric layers were identified with the aquiferous units occurring in the fourth and fifth layers respectively. Multi-aquifer types such as unconfined and semi-confined aquifers exist in the study area, resulting in good prospects for groundwater development with a potential increase towards the western parts of the study area. Finally, the protective capacity was rated as poor indicating the aquifers are vulnerable to pollution from surface infiltration. The protective capacity was positively influenced by the overburden thickness and the clay content of the geologic materials.