Groundwater quality index as a hydrochemical tool for monitoring saltwater intrusion into coastal freshwater aquifer of Eastern Dahomey Basin, Southwestern Nigeria

Saltwater intrusion into coastal freshwater aquifers is a threat to groundwater quality globally. This study aims determine the extent of saltwater aquifer Eastern Dahomey Basin (EDB), Nigeria. Groundwater chemistry was sampled and analysed for ionic ratios interpreted using hydrochemical facie evolution diagram (HFE-D), mixing index (SMI) (GQIswi). High EC TDS concentration dissolved ions showed increased salinity as result seawater in wells located around communities Seme, Lekki, Eleko, Okun-Ajah, Ode-Mahin Igbokoda. Correlation wet season also suggests higher salinities which originate partly from industrial municipal effluents especially are close river channels, while dry shows dominant influence intrusion. HFE-D revealed that mixed Na + Ca–HCO3, Na–Cl Ca–Cl dominate area due gravity-driven flow leading freshening inland coastline towards northern part basin. The SMI GQIswi areas within 3 km more sensitive based on abstraction rate depth wells. present provides information value planners policy-makers sustainable management protection resources Basin.