Evaluation of the protection and hydraulic characteristics of the aquifer formation using second order geoelectric indices and pumping test in Aghalokpe, Nigeria

Abstract

In this work, the vertical electrical sounding method and the borehole pumping test analysis were used to investigate the study area and to assess the geoelectrohydraulic parameters and aquifer protective capacity. Fifteen (15) Vertical electrical sounding (VES) stations spread across the study area with a maximum electrode separation, AB/2 of 200 m were occupied. The results provide information on aquifer electrical and hydraulic properties which included the aquifer resistivity, aquifer thickness and depth, longitudinal unit conductance, transverse resistance, hydraulic conductivity and transmissivity. The aquifer resistivity values ranged from 503–18914 Ωm, with a depth for adequate water production given as 14 m to a maximum of 22 m. The calculated longitudinal conductance and inferred protective capacity ranged from 0.0141 - 0.167 mho, indicating weak to moderate capacity. The borehole pumping test data was analysed using the Cooper-Jacob method in determining the aquifer parameters. The hydraulic conductivity (K) value mea sured from a reference well was combined with DarZarrouk parameters to estimate the transmissivity and hydraulic conductivity values of the aquifer across the area. The results showed that the aquifer transmissivity values varied from 198.8 m²/day to 1473.6 m²/day with an average of 459.8 m²/day, while hydraulic conductivity values varied from 5.7 m/day to 66.7 m/day, with an average of 31.1 m/day. These estimated parameters indicate that even though the area has high aquifer potential due to its transmissivity and hydraulic conductivity values, it is prone to contamination due to its poor protective capacity.

Keywords: Geoelectric indices, Aghalokpe, Aquifer parameters, Pumping test, Dar- Zarrouk