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No. of pages: 192

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Abstract:

This research work presents findings of the extent and distributions of saline zone and the hydrochemical characteristics of the groundwater of Awe, Keana and Giza areas in the Middle Benue Trough of Nigeria. Static water levels(swl) of hand-dug wells were measured and the results used to generate hydraulic head data and a hydraulic head map. The static water levels range from 1.0m to 13.5m at Awe, 1.0m to 4.5m at Keana and 2.2m to 9.2m at Giza. The hydraulic head maps for the three areas show different patterns/directions of groundwater flow for each area. Geophysical investigations, mainly vertical electrical sounding (VES) using Schlumberger electrode configuration array were performed at 47 locations spread across the entire study areas. Results of the VES revealed that the study areas are characterized by 3, 4 and 5geo-electrical layers with 9 different curve-type signatures. Also, results of the VES show that the Awe area has the highest occurrence of saline zone, followed by Keana and Giza respectively. Multi-layer saline zones were observed only at Awe. Thirty (30) groundwater samples (10 each from the 3 areas) were analyzed for physiochemical parameters (rare earth elements, heavy metals, major cations and major anions). Results of the hydrochemical analysis revealed five (5) hydrochemical facies namely, Ca-HCO3, NaCl, NaHCO3, Ca-Na-HCO3 and Ca-Mg-Cl facies. Principal component analysis of the hydrochemical data revealed that the groundwater chemistry of the areas is controlled by the mineralization of the host rocks, weathering of galena, uranite, feldspathic minerals and dissolution of limestone and dolomite. The spatial distribution pattern of the rare earth elements of groundwater of the study areas showed a strong positive correlation exists between brine and the elements. Uranium, however, showed a district distribution pattern which may indicate a distinct source from the other elements. Of the three areas studied, Keana has the most potable water supply. Awe and Giza groundwater have chloride (Cl), nitrate (NO3) and lead (Pb) contaminations. It was observed that the groundwater quality of the study areas is not only salinity dependent but also influenced by anthropogenic activities such as agricultural wastes and domestic waste released into the environment. Based on the irrigation water quality indexes employed, the groundwater of the areas ranges from unsuitable to suitable for irrigation purposes.