Groundwater Quality Assessment of Awe Area, Southwestern, Nigeria

Abstract

Twenty-three groundwater samples were collected from selected hand-dug wells across Awe area of southwestern Nigeria for groundwater quality assessment. The studies involved field measurement of physical parameters, groundwater sampling, analyses of major ions and measurement of the concentrations of five trace elements that included copper (Cu), zinc (Zn), arsenic (As), lead (Pb), and cadmium Cd) in the groundwater samples. The field measurement of the physical parameter showed that pH ranged between 5.1 and 6.8, TDS between 110 and 660 mg/L, and EC between 220 and 1340 µs/cm. From the chemical analytical results the concentrations of major cations in mg/L were; calcium (8.20 –12.60), magnesium (2.44 – 6.23), sodium (0.20 – 0.44), and potassium (1.10 – 4.65). For major anions, bicarbonate was between 17 and 95, carbonate 1 – 6, chloride 2.5 – 11.12 and sulphate was 0.005 – 0.205. For trace element concentrations, Cu, Pb, and Zn occurred below detection limits in most of the hand-dug wells, while the concentration of Cd was between 0.85 and 0.89 mg/L and As was between 0.002 and 0.009 mg/L in the shallow groundwater system of the area. Based on the average concentration, the ionic dominance is in the order of HCO₃>Ca>Cl>Mg>CO₃>K>Na>SO₄, while the water type is predominantly Ca-Mg-HCO₃. In comparison to world health organisation guideline for drinking water, the concentrations of the major ions are within the acceptable limits and pose no danger to human consumption. However, the water is grossly contaminated with cadmium while lead (Pb) concentration was also found to exceed the maximum permissible limit in some samples. This is a great concern for the potability of groundwater of Awe area.