Integrated Geophysical, Hydrogeological, and Hydrogeochemical Assessments of Groundwater Potentials in Ini Local Government Area, Northern Akwa Ibom State, Nigeria

This study presents an integrated geophysical, hydrogeological, and hydrogeochemical assessments of groundwater potential in Ini Local Government Area of northern Akwa Ibom State, Nigeria. Electrical resistivity survey using vertical electrical sounding (VES) method was conducted at 25 locations to evaluate aquifer potential. Hydrogeological assessments were carried out to determine aquifer parameters, while hydrochemical analyses used Piper trilinear diagrams, cross plots and multivariate statistical techniques to assess groundwater quality and facies classification. The 3-layer geoelectric model was characterized with top layer resistivity ranging from 139.8 (VES 4) to 974.20 Ωm (VES 7), thickness between 1.4 (VES 22) and 12.4 m (VES 18). First aquiferous layer with resistivity values in the range of 9 (VES 22) to 3023.3 Ωm (VES 10) and thicknesses from 35.6 (VES 14) to 100.5 m (VES 13). The second aquifer has resistivity in the range 25.8 (VES 23) to 2006.4 Ωm (VES 4) and unresolved thickness. The 4-layer geoelectric models has the top layer underlain by an aquiferous layer with resistivity and thickness in the range 23.4 (VES 1) to 1274.6 Ωm (VES 20) and 3.2 (VES 17) to 54.1 m (VES 6). The next layer hosts with resistivity and thickness ranges of 258.6 (VES 17) – 2666.4 Ωm (VES 20) and 43.6 (VES 1) – 82.7 m (VES 9) hosts an aquifer. The fourth layer with unresolved thickness had resistivity values in the range 19.3 (VES 1) – 2358.9 Ωm (VES 3) hosts an aquifer. Eleven viable locations (VES 6, 7, 8, 9, 10, 16, 17, 18, 19, 20, and 22) were identified as promising for groundwater exploitation, with values indicating fair to good aquifer potential. Elevation and static water level mean values are 92.72± 47.11 m and 37.46±19.7 m, respectively. Groundwater reserves varied between 575.00 x 106 and 18082 x 106 m3 and regional groundwater flow direction is from West to East. The hydraulic conductivity, K and the transmissivity, T values averaged 0.78 m/day and 49.60 m2/day, respectively. Average Fe concentration of 1.66±0.39 mg/L exceeded MAL of 0.37 mg/L, while average Mn concentration of 2.81±0.47 mg/L exceeded MAL of 0.2 mg/L attributable to natural geogenic sources. Water is safe for irrigation uses. The hydrochemical facies is classified into the Ca-Mg-HCO3-Cl and Mg2++Ca2+-Cl-+HCO3- water types attributed to carbonate and magnesium weathering. Gibb`s diagram showed TDS as a function of Na+/(Na++Ca2+) and Cl-/(Cl-+HCO3-), supporting the dominance of rock weathering for surface and groundwater and evaporation process for contaminated water samples. Cross plots based on chloroalkaline indices CA I and CAII showed forward ion exchange. Factor analysis and multivariate statistical analysis showed loadings suggestive of silicate and carbonate weathering. This study provides critical insights into groundwater suitability for domestic and agricultural uses to support sustainable water resource development given the complex geology of the study area. Preliminary geophysical investigations are recommended before borehole drilling to minimize failure risks.