Comprehensive Study of Groundwater Hydrochemistry, Driving Forces, and Health Risks in Representative Rural Agglomerations, Northern China

Abstract

Groundwater resources are the main sources of water for agricultural production and livelihoods in rural agglomerations (RA) in northern China. In 2018 and 2020, 44 and 28 sets of various groundwater samples were systematically collected, respectively, to advance scientific research and enhance the management of groundwater resources. The study employed the following research methods: Gibbs diagrams, ion ratio relationships, and multivariate statistical analysis. Additionally, the entropy weighted water quality index (EWQI) method was used to assess and compare groundwater quality, and the nitrate hazard quotient (HQ_NO3) was employed to evaluate the potential risk of nitrate pollution to different populations. The research results show that the groundwater in the RA is mostly neutral to slightly alkaline, with TDS levels between 219.45 and 857.34 mg/L. The main ions are HCO₃ ^- and Ca²⁺. Pore water has more cations and higher levels of F^-, Cl^-, and HCO₃ ^- but less SO₄ ^2- and NO₃ ^- compared with karst water. The total hardness of the groundwater is between 190.14 and 633.10 mg/L, making it moderately hard. The groundwater is mainly of the HCO₃-Ca·Mg type. The chemical composition and sources of groundwater are influenced by factors such as the weathering of carbonate rocks dominated by dolomite, reverse cation exchange, agricultural activities, and discharge of domestic sewage. Fertilizers and sewage are key in forming the chemistry of karst/fissure water, while fertilizers and manure mainly affect pore water. The groundwater quality in the RA is generally good to very good, but the increasing nitrate levels annually pose a high potential risk to infants. Areas with medium to high risk are mostly in urban and residential areas. Analyzing the EWQI/HQ_NO3 assessment outcomes of groundwater chemical parameters between 2018 and 2020, the quality of drinking water showed an improving trend.