Study on Groundwater Cycle in Beijing Pinggu Basin Based on Isotopes and Hydrochemistry

Based on the analysis of groundwater isotope and water chemical sampling in the region, the evolution characteristics of groundwater circulation in the alluvial fan of Juhe and Ruhe rivers in Pinggu were studied. The analysis results show that the pH value of the water sample is between 7.6 and 8.2, which is neutral water. The cationic content is mainly Ca²⁺ and Mg²⁺, accounting for more than 70%, and the anionic content is mainly HCO₃^–, accounting for more than 82%. The water chemical type of the groundwater samples is HCO₃•Ca•Mg. In the study area, the stable isotope content of shallow quaternary loose pore water is (δ²H: 64.9 ‰, δ¹⁸O: 9.08 ‰), the meanstable isotope content of deep quaternary loose pore water is (δ²H: 67.6 ‰, δ¹⁸O: 9.97 ‰), and the stable isotope content of bedrock karst water is (δ²H: 64.6 ‰, δ¹⁸O: 9.36 ‰). The average stable isotope content of bedrock karst water is close to that of shallow groundwater. The ¹⁴C content of shallow quaternary loose pore water is 46.7%～93.1%, that of deep quaternary loose pore water is 40.23%～61.13%, and that of bedrock karst water is 53.7%～89.2%,which is close to that of shallow Quaternary loose pore water.Through the analysis and research to master the Beijing pinggu basin groundwater circulation evolution, basin quaternary pore water and concealed rock karst water hydraulic connection, research results for pinggu basin groundwater hydrogeological conceptual model and hydrogeological parameters of a preliminary determination, evaluation of groundwater resources calculation provides the technical support.