Geophysical and physicochemical investigation of groundwater repositories in Njaba LGA of Imo State, eastern Nigeria

Abstract

Geoelectric survey integrated with physicochemical method of water analysis was used to investigate the aquifer repositories in Njaba, Imo State, eastern Nigeria. This was done in 15 locations using vertical electrical sounding (VES) employing Schlumberger electrode configuration, and water samples from four boreholes were analyzed in the laboratory. The resistivity data were interpreted using forward and iterative least square inversion modeling of WINRESIST software. Four to six geoelectric layers and the VES characteristic curve types were obtained. The resistivity values vary across the study area with their respective depths and thicknesses. The aquifer resistivities range from 402.50 to 16,484.40 Ωm. The hydraulic parameters estimated include: Dar Zarrouk parameters (longitudinal conductance and transverse resistance), hydraulic conductivity and transmissivity. The longitudinal conductance ranges between 0.0004 and 0.0763 Ω−1, and transverse resistance ranges between 6823.40 and 245,320.00 Ωm2. The range of hydraulic conductivity and transmissivity varies from 0.0450 to 1.4363 m day−1 and 0.3195 to 44.0944 m2 day−1, respectively. The contour maps generated using Surfer software package displayed the variations of these parameters across the study area. The results obtained indicate that the study area has low groundwater potential based on the transmissivity values and may be prone to surface contamination due to its poorly protected aquiferous units. The concentrations of the ions in the water samples measured were compared with the World Health Organization (WHO) standard for drinking water and were found to be below WHO standard. The sodium percentage and sodium absorption ratio were calculated in order to determine the suitability of the groundwater for agriculture.