Hydrochemical characteristics and sources of groundwater pollution in Soubré and Gagnoa counties, Côte d’Ivoire

Abstract

For many years, groundwater has been widely used to meet a variety of human needs. As a result of increased urbanization, industrial use, and agriculture, groundwater is inextricably affected by various threats, resulting in groundwater pollution. This current study was carried out to determine the hydrochemical characteristics of groundwater in Gagnoa and Soubré counties as well as the main sources of pollution and their impact on groundwater chemistry and quality. A total of thirty (30) groundwater samples were collected from boreholes in September 2020. The following physicochemical and chemical parameters were analyzed: Na, Ca, K, Mg, SO4, NO3–N, HCO3, Cl, pH, EC and TDS. The results showed that groundwater was acidic with a pH range from 5.22 to 6.84, fresh and moderately mineralized with a TDS range from 55.96 to 744.46 mg/l. Hydrogeochemical characterization based on the Piper diagram and Gibbs plot was used to identify the groundwater types and the main mechanism controlling the groundwater mineralization. Five (5) water types were identified with the dominance of hydrogen carbonate facies and showed the presence of silicate weathering and carbonate dissolution in the area. This is consistent with the results inferred from Gibbs plot showing that groundwater chemistry is governed by rock-water interaction. The spatial distribution map of major ions showed the different locations where each ion is dominant.According to WHO standards, the parameters show values within the threshold limit except for some of them of which their values exceed the limit. Principal component analysis and ionic ratio plots showed that the high values of nitrate as nitrogen and sulfate observed are due to the influence of natural sources such as carbonate dissolution and anthropogenic activities such as sewage-manure and chemical fertilizers.Therefore, mitigation measures should be adopted to reduce the impact of human activities contributing to groundwater pollution to protect the groundwater quality and human health.