Identification of hydrogeochemical processes in groundwater using major ion chemistry: a case study of Yenagoa and environs, southern Nigeria

Abstract

Hydrogeochemical studies were carried out in Yenagoa city and environs, Southern Nigeria in order to assess the chemistry of the groundwater and identify the dominant hydrogeochemical processes and mechanisms responsible for the evolution of the chemical composition of the groundwater. The study approach includes detailed geochemical analysis of groundwater samples collected from domestic boreholes for major constituents such as Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃, Cl^-, SO₄ ^2-, and NO₃^- and the hydrochemical data was subjected to multivariate statistical analysis and conventional graphical plots. The results show that most groundwater quality parameters are within World Health Organization acceptable limits for drinking water. The chemical relationships of the ions in Piper diagram identify Ca- Cl, Ca-HCO₃ and Na-HCO₃ as most prevalent water types. The alkalis exceed the alkaline earths and weak acids exceed the strong acids. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO₃ indicates the dominance of silicate weathering as the major source of cations. The plot of Na vs Cl indicates higher Na, derived from silicate weathering process which was also supported by higher HCO₃ values. Reverse ion exchange process is also significant in the study area which is indicated by negative Schoeller indices and shifting to the left in the plot of Ca²⁺ + Mg²⁺ vs HCO₃ + SO₄. Furthermore, the plot of Na-Cl vs Ca+Mg – HCO₃ – SO₄ confirms that Ca, Mg, and Na concentrations in groundwater are derived from aquifer materials. Saturation index of silicate and carbonate minerals indicate undersaturation to oversaturation

KEYWORDS: Groundwater, ion exchange, rock-water interaction, saturation index, Yenagoa