Hydrogeochemical Assessment of Groundwater around Gauta, Central Nigeria

Abstract

The present study was aimed at assessing the hydrogeochemical characteristics of groundwater with a view to identifying key processes controlling groundwater chemistry and in so doing identify any quality concerns. A total of 30 water samples were analysed for concentrations of major ions (Ca2+, Mg2+, Na+, K+, SO4 2-, HCO3 - , CO3 - and Cl- ); while in-situ measurements of pH, temperature, total dissolved solids TDS and electrical conductivity EC were made. Conventional graphical plots (Gibbs, Piper, and ionic ratios) of ionic concentrations in the groundwater were used to characterize water Facies and identify major processes responsible for the ionic assemblage. The study area is underlain by two main rock types, schist and gneiss. Dominance of cations is in the order: Na+>Ca2+>Mg2+>K+; while that of the anions is in the order: HCO3 - >SO4 2-> Cl- >CO3 - . Groundwater in the study area is characterized by four types: Na-Cl type (33%); Mixed Ca-Mg-Cl type (30%); Mixed Ca-Na-HCO3 type (27%) and Mg-HCO3 type (10%). Gibbs plot indicated that the ions were mainly sourced from rock-water interaction through dissolution and leaching of the gneisses and schists of the study area. However, relatively high concentration of Cl may be due to anthropogenic activities, hence the Na-Cl water type. In terms of quality for domestic purposes, concentrations of analyzed ions and the physical parameters are within the permissible limits of both WHO and SON (NSDWQ, 2007), with the exception of a few locations that had high pH (up to 9.2) and another location with a high TDS concentration (1040mg/L). Assessment for irrigation purposes using indices such as SAR, PI, RSC and %Na show that most of the groundwater samples were suitable for use as source of water for irrigation.