Integrated groundwater potentials studies, aquifer hydraulic characterisation and vulnerability investigations of parts of Ndokwa, Niger Delta Basin, Nigeria

Abstract

Field geological and geophysical (Vertical Electrical Sounding VES) survey data were used in investigating groundwater potentials, aquifer characteristics and vulnerability in parts of Ndokwa area, Niger Delta, Nigeria. Data from twenty-one (21) representative VES survey points using Schlumberger configuration were acquired, processed and interpreted. Pumping test data and litho-log data from existing boreholes in the area were used to constrain interpretation and correlation of the VES results. The results revealed five to six geo-electric layers/units across the study area. The subsurface lithology is predominantly sandstone intercalated, in some cases, with clay, sandy clay, and clayey sand. Results also revealed the average depth to aquifer as 71.91 m (10.33–173.97 m); average aquifer thickness as 42.52 m (4.7–149.7 m) and average aquifer resistivity value as 1289 Ωm (470.84–2697.7 Ωm). Average overburden thickness was estimated to be 28.53 m (4.28–62.44 m). Aquifer characteristics derived from the VES results gave average calculated aquifer transmissivity value as 1162.31 m2/day (129.54–4181.31 m2/day), and average calculated aquifer hydraulic conductivity as 27.28 m/day (25.69–28.92 m/day). Longitudinal conductance values range of 0.006–0.137 were recorded from geo-electric field survey data in the area, indicating dominance of sand and sparse distribution of clay; and suggesting that the Aquifer Protective Capacity APC of the overburden above the aquifers in the study area is mostly poor to weak and prone to contamination from infiltration. The DRASTIC model was applied to ascertain the DRASTIC Index and compute aquifer vulnerability distribution of the area; and it revealed that the study area is characterised by low – moderate – high vulnerability at different locations. Topsoil corrosivity studies showed that topsoil in the area is practically non-corrosive to slightly corrosive. The results of this study have implications for groundwater resources development and management in the study area. Keywords: Groundwater development, Aquifer vulnerability, Hydraulic characterisation, Geo-electric survey, Niger Delta