INTEGRATED GEOPHYSICAL, HYDROGEOLOGICAL AND HYDROGEOCHEMICAL ASSESSMENTS OF GROUNDWATER POTENTIALS IN IBIONO IBOM LOCAL GOVERNMENT AREA OF NORTHERN AKWA IBOM STATE, NIGERIA

This study presents an integrated geophysical, hydrogeological, and hydrochemical assessment of groundwater potentials in Ibiono Ibom Local Government Area of northern Akwa Ibom State, Nigeria. An electrical resistivity survey was conducted at 39 locations to evaluate aquifer potentials using geoelectrical data. Hydrogeological assessments were carried out to determine aquifer parameters, while hydrogeochemical analyses used Piper trilinear diagrams, Gibbs cross plots and multivariate statistical techniques to assess groundwater quality and facies classification. The 3-layer model is characterized with top layer resistivity from 85.6 Ωm (VES 28) to 1104.9 Ωm (VES 27), layer thickness varied between 0.4 m (VES 1) and 14.3 m (VES 36). Underlying this is a layer of with resistivity values from 812.3 Ωm (VES 34) to 2910.7 Ωm (VES 18) with layer thickness from 9.7 m (VES 1) to 83.2 m (VES 28). Underlying this is a layer with resistivity in the range 102.5 Ωm (VES 18) to 2893 Ωm (VES 34) with unresolved layer thickness. Lithologically, the top layer does not constitute any water bearing medium with underlying layer of unresolved thickness having some conductive zones. The 4-layer geoelectric model has the first layer with thickness and resistivity from 0.8m (VES 10) to 7.3m (VES 26) and 9.2 Ωm (VES 3) to 2312.9 Ωm (VES 17). It is underlain by a layer with resistivity and thickness from 24.8 Ωm (VES 12) to 2943.1 Ωm (VES 32) and thickness 1.4m (VES 11) to 37.4 m (VES 25). The next layer with resistivity and thickness of 23.6 Ωm (VES 9) –4183.2 Ωm (VES 15) and 8.9m (VES 11) – 136.7.4m (VES 26). The fourth layer with unresolved thickness had resistivity values in the range 4.3 Ωm (VES 10) – 2218.0 Ωm (VES 37). Second, third and fourth layer constitutes the aquifers. The 5- layer geoelectric model has top layer with resistivity and thicknesses from 504.3 Ωm (VES 2) – 2315.2 Ωm (VES 21) and 0.6m (VES 6) – 1.7 m (VES 2). It is underlain by a resistive layer with resistivity and thickness from 64.4 Ωm (VES 2) – 412.6Ωm (VES 6) and 5.3m (VES 21) – 12.4 m (VES 2). Next is a conductive layer with resistivity and thickness of 281.7 Ωm (VES 2) – 1417 Ωm (VES 21) and 8.4m (VES 21) – 17.8 m (VES 2). This is underlain by a highly conductive layer having thickness from 48.6 m (VES 21) – 57.6 m (VES 6) and resistivity from 57.2 Ωm (VES 6) – 117.6 Ωm (VES 2). The fifth geoelectric layer with unresolved thickness had resistivity in the range 11.1 Ωm (VES 2) – 1205.5 Ωm (VES 21). The fourth and fifth layers constitute the aquifers. Thirty three (33) locations (VES 1,5,6,7,8,9,11,12,13,14,15,16,17,18,19,20,21,22,24,25,26,27,28,31,34,35,36,37 and 38 were identified as promising for groundwater development. Elevation and static water level mean values are 140.13±77.37m and 32.46±17.95m, respectively. The hydraulic conductivity K, averaged 13.28 m/day and the transmissivity T, range from 252.32-1932.24 m2/day (average 413.78 m2/day) for the study area. Groundwater reserves varied between 928.00 x 106 and 64178 x 106 m3 and regional groundwater flow direction is from North to South. Average Fe concentration of 1.67±0.10 mg/L exceeded MAL of 0.37 mg/L. Water is safe for irrigation uses. The hydrochemical facies is classified into 3 groups; the Ca-Mg-HCO3-Cl, Mg2++Ca2+-Cl-+HCO3- and Ca2+-Mg2+-SO42–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-). Gibbs 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.