Wolong Town, Pingquan City, is located in a typical low-mountainous area of northern China, where groundwater is a crucial drinking water resource, thus, investigating groundwater’s hydrochemical characteristics and assessing nitrate-related health risks are vital for protecting, developing, and utilizing water resources. In this study, 66 groundwater samples were collected and analyzed for physicochemical parameters and major ion concentrations. Results showed that the groundwater in Wolong Town was weakly alkaline (average pH = 7.6), and classified as fresh water with TDS ranging from 90.0 to 900 mg/L. The dominant hydrochemical type was identified as HCO₃⁻-Ca²⁺. Hydrochemical evolution was jointly regulated by natural water-rock interaction, anthropogenic nitrogen input, and environmental redox differentiation. Among these, water-rock interaction was the primary driver, where the hydrochemical composition was mainly shaped by the dissolution of halite, calcite, dolomite, and gypsum, coupled with cation exchange. Nitrate was the primary groundwater pollutant, with concentrations varying from 0.94 to 259 mg/L; elevation, soil type, and population density were key drivers influencing nitrate distribution. Health risk assessment indicated that nitrate posed significantly higher non-carcinogenic risks to infants and children than to adults, and long-term consumption of groundwater with excessive nitrate might induce adverse health effects. This study enhances understanding of shallow groundwater’s hydrochemical evolution and nitrate contamination-related health risks, thereby providing theoretical support for the sustainable development, utilization, and quality protection of groundwater resources in semi-arid low-mountainous areas.

The evolution of groundwater in the Puhe River Basin is closely related to the ecological security of the Beijing–Tianjin–Hebei water source conservation zone. Based on 122 groundwater samples, this study systematically investigated the hydrochemical characteristics, evolution mechanisms, and water quality of shallow groundwater using mathematical statistics, Piper diagrams, ionic ratio analysis, and a variable fuzzy pattern recognition model. The results showed that shallow groundwater in the middle and upper reaches is generally weakly alkaline, fresh to hard water, with HCO₃–Ca and HCO₃·SO₄–Ca as the dominant hydrochemical facies. Groundwater hydrochemistry is primarily controlled by rock weathering, and the dissolution of silicate and carbonate rocks is the main source of major ions. Calcite and dolomite are in dynamic equilibrium between dissolution and precipitation, whereas gypsum and halite remain undersaturated. Overall, groundwater quality is generally good; however, anthropogenic activities in cultivated and construction lands have altered local hydrochemical composition and caused water quality deterioration in some areas. These findings improved the understanding of groundwater hydrochemical evolution in typical small watersheds of the northern Hebei hilly region and provided a scientific basis for the sustainable management and protection of groundwater resources in the Beijing–Tianjin–Hebei water source conservation area.

Soil pH is a fundamental geochemical parameter with direct implications for environmental quality, but its spatial drivers in geologically complex mountain regions remain poorly understood. This study investigated surface soil pH across 452 sites in Pingquan City, a semi-arid, lithologically heterogeneous mountainous area of Hebei Province, China. The results show that the soil in Pingquan City is predominantly alkaline, with higher pH in southwestern and northeastern areas and lower pH in the northwest. Soil pH ranged from 4.62 to 9.98, with strong positive spatial autocorrelation. Comprehensive quality assessment indicated that the overall soil quality is moderately low. GeoDetector analysis identified average annual temperature, soil texture, elevation, and bedrock lithology as dominant structural drivers, with bi-factor enhancement interactions. GeoSHAP further uncovered two local effects: precipitation exerts a positive influence on pH in carbonate-rock-dominated areas, reversing the leaching–acidification pattern; and temperature functions as a proxy variable integrating co-varying topography, parent material, and texture rather than a direct thermal driver. The combined application of spatial autocorrelation, GeoDetector, and GeoSHAP provides an effective framework for identifying spatial phenomena, discriminating dominant drivers, and explaining local variations. These findings support regional soil quality assessment and land management, and provide a geochemical baseline for safeguarding groundwater resources in mountainous regions.