Geochemical and isotopic evidence for palaeo-seawater intrusion into the south coast aquifer of Laizhou Bay, China

► Hydrochemistry, multi-isotopes, and hydraulic data were used to study saltwater intrusion. ► Salt sources and their contributions to the salinity distribution are identified. ► Groundwater age and mixing behavior are estimated. ► Hydrogeochemical evolution of different types of groundwater is determined. ► Multi-approach study can improve the understanding of reactive transport processes.