Hydrogeochemistry of Artesian and Controlled Shallow Wells’ Water: A Case Study of Ikere-Ekiti, Southwestern Nigeria

Abstract

Hydrochemistry of water from artesian and controlled shallow wells at Ikere-Ekiti was carried out to elucidate the wells’ water quality status and hydrochemical evolution. Water samples from fifteen wells (5 artesian wells and 10 controlled shallow wells) were collected in duplicates into pre conditioned polyethylene bottles. The samples for cations analysis were acidified with concentrated HNO3 to a pH of 2 and cations and anions determinations were carried out employing Atomic Absorption Spectrophotometer and Colorimetric method using Spectrophotometer respectively. Prior to sampling, at each location, in-situ parameters (pH, temperature (°C), EC (µS/cm) and TDS (mg/L) were obtained using Multiparameter portable Meter. Results of this study revealed that all water samples in the area have pH<7 and are acidic. The Total Hardness indicated that all water samples from artesian wells fell into the very hard water category while eight (80%), one each of the water samples from the controlled shallow wells were in the moderately hard, hard and very hard water classes respectively. All the measured chemical parameters had concentrations within approved standard of drinking water except for the NO3- values that were above 50mg/L for all water from the controlled shallow wells. The order of increased cations concentrations in the Artesian Wells’ water was Ca2+>Mg2+>K+>Na+ as against Ca2+>Mg2+>Na+>K+ in the controlled shallow wells’ water. As for the anions, order of concentrations (SO42->NO3->Cl->HCO3-) was the same. Differences in the order of ionic concentrations were due to lithologic variations as well as differential weathering. The hydrochemical evolution of groundwater in the study area was controlled solely by weathering and water in the study area was the CaCl type. The physico-chemical parameters were both positively and negatively correlated among themselves and ions in the groundwater of the study area are both from the geogenic and anthropogenic sources. There is no significant difference between water from the artesian and controlled shallow wells as water from them are low mineralized with most physico-chemical parameters falling below approved standards for drinking water. However, the acidic nature of all sampled water as well as high NO3- concentrations call for caution and further investigations.