Abstract: Shenmu City, located in the contiguous region of Shanxi, Shaanxi, and Inner Mongolia, is a nationally important energy, chemical, and mineral base. Under the dual influences of natural conditions and human activities, water environment problems have become increasingly prominent in this region. Investigating the hydrochemical characteristics and their genesis can provide a scientific basis for the rational development and protection of surface water and groundwater. In this study, we collected 167 groundwater samples (157 well water samples and 10 spring water samples) and 30 surface water samples in Shenmu City in July 2024. Ion concentrations were measured to analyze the hydrochemical characteristics of surface water and groundwater and to understand the formation mechanisms. The results showed that pH of surface water and groundwater in Shenmu City ranged from 7.0 to 8.6, being generally neutral to weakly alkaline. Total dissolved solids (TDS) concentrations ranged from 129.4 to 2928.9 mg·L^-1, with fresh water being dominated. The pH (7.8), electrical conductivity (EC) (858.3 μS·cm^-1), and TDS (513.1 mg·L^-1) of surface water were all higher than those of groundwater. The dominant anion was HCO₃^-, and the dominant cations were Ca²⁺ and Na⁺. Coal mining led to localized enrichment of Na⁺, Cl^-, and SO₄^2- in both surface water and groundwater, particularly evident in Daliuta Town and Dianta Town. The hydrochemical types of both surface water and groundwater were different. Surface water was dominated by the HCO₃Ca·Mg type, while groundwater was dominated by the HCO₃Ca·Na type. In coal mining areas, surface water and groundwater were enriched in Na⁺ and SO₄^2-, and the hydrochemical types were mainly HCO₃·SO₄Ca, HCO₃·SO₄Ca·Mg, and SO₄·Cl·HCO₃Na. The hydrochemical characteristics of surface water and groundwater were controlled jointly by natural processes and human activities. Natural factors included rock weathering, cation exchange, and evaporation-crystallization, with water-rock interactions dominated by the dissolution of silicate and carbonate minerals. Among the human activities, industrial and mining activities exerted the dominant influence on water bodies, followed by agricultural activities. As water bodies in the energy base have been affected by industrial activities, strict environmental protection measures should be adopted to safeguard the health of the local water environment.

Key words: Shenmu City, hydrochemistry, ion source, control mechanism