This paper is the result of hydrogeological survey engineering.

Objective The study on the characteristics of groundwater chemical evolution and its control factors in coastal zones is of great significance for the sustainable utilization of groundwater resources in coastal cities.

Methods On the basis of field investigation and comprehensive analysis of historical data, the characteristics of groundwater chemical evolution in Wenzhou Plain were systematically analyzed by using hydrochemical diagram, ion proportional relationship, multivariate statistical analysis and environmental isotope methods, and the main controlling factors affecting groundwater chemical evolution were discussed.

Results (1) Phreatic water in Wenzhou Plain was dominated by fresh water, and HCO₃^–, Na⁺ and Ca²⁺ were the predominant ions. However, confined water is brackish and salt water, and Cl^– and Na⁺ were absolutely dominant ions. (2) From the mountain front to the marine deposition plain, the transition from low−salinity HCO₃ type water to high−salinity Cl type water in the study area is mainly controlled by natural processes, and human activities caused abnormalities of local groundwater chemistry. (3) On the ten−year scale, the content of the main components of phreatic water decreased to a certain extent, and the hydrochemical type evolved in the direction of the decrease of Cl^– and the increase of HCO₃^–. (4) Natural factors such as water−rock interaction, seawater interaction, redox environment and human factors such as industrial and agricultural production and domestic sewage are the main controlling factors of groundwater chemical evolution in Wenzhou Plain.

Conclusions The results of groundwater health risk assessment show that certain potential non−carcinogenic risks of groundwater exist in the area, the non−carcinogenic risk of phreatic water is less than that of confined water, drinking water intake is the main way to harm human body, and the non−carcinogenic risk of children in the same environment is higher than that of adults. Therefore, it is necessary to conduct long−term monitoring of groundwater with health risks and strengthen groundwater resource management and pollution prevention in such areas.