[Analysis on Hydrochemical Evolution of Shallow Groundwater East of Yongding River in Fengtai District, Beijing].

In order to enhance the support for groundwater development and utilization, as well as pollution control and prevention in Fengtai District, Beijing, a comprehensive study was conducted based on long-term monitoring data of shallow groundwater in the eastern area of Yongding River during the dry season. The mathematical statistics, Piper diagram, Gibbs diagram, and ion ratio analysis and other methods were employed to explore the pattern of groundwater hydrochemical evolution, the formation mechanism, and sources of pollution in Fengtai District. The findings were as follows:① Overall, the current groundwater quality in the study area was poor. The average concentration of each index in groundwater increased and then decreased from 1976 to the present. The pollution range of Cl