Hydrogeochemical study of Shallow Groundwater of Oyo Town Southwestern Nigeria

Abstract

Groundwater is the only reliable water supply for human population in Oyo Town, hence; studies of major ions concentrations and measurements of supplementary parameters were carried out in samples from twenty (20) hand dug wells across the area using flame photometry and spectrophotometry methods. The aim is to assess the quality of the water for human consumption. From well inventory, the depths of the hand-dug wells ranged between 6.6 and 26.5 m. The chemical analyses results showed that water samples from quartzite and quartz schist were more mineralized with TDS average of 612 mg/L than those from migmatised biotite gneiss and undifferentiated gneiss complex terrain with TDS of 530 mg/L and 133 mg/L respectively. Also, the measured water acidity/alkalinity is lower in terrains underlain by varieties of gneissic rocks than those from quartzite areas. The general range of major ions in mg/L were: Ca2+10.9 – 126.5; Mg2+ 1.8 – 25.2; Na+ 6.5 – 76.2; K+ 0.9 – 80.0; HCO3- 58.0 – 434.0; Cl-- 2.0 – 62.6; SO42- 3.0 – 81.0 and NO3- 0.9 – 19.1. The dominant hydrochemical facies is the Ca- HCO3- water type. Considering the fact that the wells are shallow, nitrate concentrations can be said to be low with values between 0.9 and 19.1 mg/L, while chloride was between 2.0 and 62.6 mg/L. Though, the concentrations of all the ions are not worrisome; enrichment of nitrate and chloride in water often suggests human inputs. There is a strong and positive correlation between TDS and major ions, whereas nitrate and chloride have low relationships with the major ions suggesting possible anthropogenic source for the duo.