Abstract

This study involves the determination of the hydrochemical character and quality of springs, shallow and deep wells around the Okemesi fold belt, south western Nigeria. This is with a view to elucidate their nature, type and evaluate portability, and suitability for agricultural and industrial purposes. The Okemesi fold belt is underlain by schistose rocks, mainly mica schist, quartz schist, and quartzite with minor amphibolites and gneisses.

The major hydrochemical water type are Na – ( K ) – Cl – ( SO₄ ) and Ca – (Mg) – ( Cl ) – SO₄ water facies constituting about 52% and 47% respectively. The study showed that almost all of the physico-chemical parameters such as total dissolved solid TDS (18.75 - 790.50 mg/l), electrical conductivity EC (25 - 1054 ?s/cm), pH (5.4 - 7.4), temperature (24.8 - 29.5°C), turbidity (2.2 - 40.5 N.T.U), total hardness (10 - 274 mg/l), total alkalinity (18 - 274 mg/l), dissolved oxygen (1.8 - 7 mg/l), chlorine demand (1.56 - 4.75 mg/l); and bacteriological analysis (5 - 80 MPN) results were within the World Health Organization (WHO) limits recommended for drinking water. However, some groundwater samples have Ni⁺ and K⁺ concentrations slightly above the recommended standard.

These physico-chemical parameters, especially cations: Ca²⁺ (1.6 - 72.8 mg/l), Mg²⁺ (0 - 4.39 mg/l), Na⁺ (1.63 - 75.0 mg/l), K⁺ (0 - 108.3 mg/l) , Si (4.0 - 10 mg/l), Cu (0 - 0.391 mg/l), Zn (0 - 0.29 mg/l), Cd (0 - 0 mg/l), Pb (0 - 0 mg/l), Fe (0.1 - 0.1 mg/l), Ni (0 - 0.043 mg/l) and anions such as HCO₃ (6.1 - 79.3 mg/l), Cl^- (5 - 109 mg/l), SO₄^2- (38 - 76 mg/l), NO₃^2- (0 - 0 mg/l) and PO₄^3- (0.005 - 0.03 mg/l) seem to reflect the chemical nature of the underlying rock units suggesting dissolution, weathering and water – soil / rock interaction processes.

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