Origin of groundwater salinity and hydrochemical processes in an unconfined aquifer: case of Yang-Dai River basin in Qinhuangdao (China)

Abstract

Groundwater salinization has become a growing concern in Yang-Dai River basin of Qinhuangdao (China) where groundwater is commonly exploited for domestic, industrial and agricultural uses. In this study, hydrochemical and physical parameters of groundwater were analyzed to identify the origin of groundwater salinity and the geochemical processes occurring in the unconfined aquifer. Groundwater types are Ca·Mg–HCO3·SO4 in the hills, Ca·Mg–HCO3·SO4 in the piedmont plain and Na–Cl in the coastal alluvial plain, respectively. Electrical conductivity values varied between 322 and 3990 μS/cm. Chloride concentration attained to 942 mg/L and the proportion of seawater intrusion in the coastal alluvial plain was 5.39 % calculated by seawater fraction formal, displaying the severe seawater intrusion. Cation-exchange reactions and water–rock interactions related to the dilution of halite, gypsum, dolomite and calcite occurred by ionic relationships during seawater intrusion. High nitrate concentrations ranged from 35.6 to 686.5 mg/L distributed in the hills and the south coastal alluvial plain where they are seriously polluted by the industrial wastewater, agricultural fertilizers and domestic sewage. Seawater intrusion and nitrate contamination have common effects on the hydrochemical process in the south coastal alluvial plain. Therefore, the origin of groundwater salinization was attributed not only to seawater intrusion but also to anthropogenic pollution in the study area. This research provides useful information for groundwater salinization and water planning strategies in a coastal area.