Hydrochemical types, characteristics, formation mechanism and exploitation potential of shallow groundwater in the plain south of Beijing-Tianjin

Objective This paper aims to conduct an in-depth study on the hydrochemical types, characteristics, formation mechanisms, and development and utilization potential of shallow groundwater in the plain area south of Beijing and Tianjin, so as to provide a theoretical basis for the management and protection of regional water resources.

Methods Groundwater surveys, water sample collection and analysis were carried out in Shijiazhuang, Hengshui, Cangzhou and other areas of the Hebei Plain. Methods including Gibbs model simulation, hydrochemical analysis, major ion ratio analysis, and saturation index calculation using the PHREEQC software were comprehensively applied to analyze the hydrochemical characteristics, water-rock interaction mechanism and development and utilization potential of groundwater.

Results The results show that along the groundwater flow direction, from the alluvial−proluvial zone, through the pre−fan depression zone, to the inter−river channel zone of the central plain, the total dissolved solids (TDS) and concentrations of Na⁺, Ca²⁺, Mg²⁺, Cl⁻ and SO₄²⁻ increase gradually. The pH first increases and then decreases, while the contents of K⁺ and HCO₃⁻ first decrease and then increase. The groundwater hydrochemical type evolves from HCO₃−Ca type to Cl·SO₄−Ca·Mg type and then to Cl·SO₄−Na type. Hydrochemical components in the alluvial-proluvial zone are mainly controlled by carbonate dissolution; the pre-fan depression zone is jointly affected by water-rock interaction and evaporation-crystallization, dominated by silicate weathering; and the central inter-river zone is controlled mainly by halite dissolution and evaporation-crystallization.In terms of exploitation status, shallow groundwater in the freshwater zone is over-exploited, whereas the saline water zone has abundant natural water resources but limited available freshwater.

Conclusions Shallow groundwater in the plain south of Beijing and Tianjin is affected by multiple factors during runoff. The upstream alluvial−proluvial zone is strongly influenced by human activities, and the impact of domestic sewage requires attention. Exploitation of shallow groundwater in the freshwater zone should be strictly controlled. Comprehensive utilization of brackish water (2~3 g/L) can be strengthened in the saline water zone.