Characteristics and causes of hydrochemical evolution of deep groundwater in the Luanhe Delta

Analyses of hydrochemical evolution of groundwater can provide a scientific basis for conservation and sustainable development of groundwater recourses. The third aquifer in the Luanhe delta region is taken as an example, and two hydrogeological profiles are selected to analyze the characteristics of hydrochemical constituents. Piper diagram is used to examine the hydrochemical differences in groundwater from upstream to downstream. Hydrochemical types change from Ca·Na-HCO3 type in the upstream to Na·Ca-HCO3·SO4 and Na-HCO3·Cl types in the downstream. In the upstream, incongruent dissolution mainly occurs along the groundwater flow direction, causing simultaneous increases in concentrations of HCO-3 and Ca2+ + Mg2+, as well as simultaneous increases in concentrations of Cl-+SO2-4 and Na+. In the downstream, in addition to incongruent dissolution, cation exchange and desulphidation may also occur, leading to decreases in concentrations of Ca2+, Mg2+ and SO2-4, and increases in concentrations of Cl- and Na+. This research provides a better understanding of the hydrochemical evolution of deep groundwater from the piedmont to the coastal region.