LAUSR

Hydrochemical investigation of groundwater was carried out on the coastal aquifers of Ogun Waterside, Southwestern Nigeria. Groundwater samples were collected and assayed for physicochemical parameters during wet season (August, 2016) and dry season (March, 2017). The analysed data were further subjected to correlation analysis (CA), principal component analysis (PCA), hydrochemical facies and descriptive statistics. Results revealed that the groundwater is slightly acidic with fresh to saline character. The CA showed very strong associations between TDS, EC and Cl concentrations in both wet and dry seasons. PCA confirmed the main factor influencing the groundwater chemistry in the study area to be component I (salinity component). Piper plots also revealed that the aquifer is mainly of Na−Cl water type. Schoeller and Stiff diagrams showed that the groundwater comprises relative abundance of major ions in the following order: Na+>K+>Mg2+>Ca2+ for the cations and Cl−>HCO3−>SO42− for the anions. Thus, the primary process influencing the hydrochemistry of the study area is saltwater invasion while mineral dissolution and rainwater infiltration play less significant roles. Most parameters fall within the permissible limit proposed by the World Health Organization (2011) and Nigerian Standard for Drinking Water Quality (2007). However, higher concentrations of chloride and bicarbonate ions observed towards the southern flank of the study area suggest signs of impairment. Assessment of the sampled water for agricultural purposes with respect to salinity hazard, Total Hardness (TH), percentage sodium (%Na) and Sodium Adsorption Ratio (SAR) revealed that the water is suitable for agricultural activities.