Hydrogeochemical processes and quality assessment of shallow groundwater in Chenqi coalfield, Inner Mongolia, China

In mining areas, fresh groundwater plays an essential role in meeting the water needs for coal production, agriculture, animal husbandry, and human consumption. The objective of this study is to obtain a deeper understanding of the groundwater evolution processes, and to assess the groundwater quality and its suitability for domestic and irrigation purposes in Chenqi coalfield, located in the Hulunbuir grassland of Inner Mongolia, China. 21 groundwater samples were collected from three different landforms (high plain, plain, and river valley) for major ions and trace metals analyses. General hydrochemistry, correlation, and hierarchical cluster analysis methods were employed. The results show that the groundwater is predominantly of the HCO₃–Na·Ca type and HCO₃–Ca·Na in the plain and river valley areas, and of the Cl·(HCO₃·SO₄)–Na·Ca in the high plain area. The groundwater circulation is regulated by natural processes: in the plain and river valley areas, rock weathering, dissolution of silicates (especially plagioclase), and reverse cation exchange are the major hydrogeochemical processes occurring, whereas, in the high plain area, evaporation and dissolution of halite, silicates, and gypsum are the main hydrogeochemical processes. Besides, mining activities have a certain impact on groundwater quality due to the change of groundwater circulation conditions. Groundwater in the plain and river valley areas is suitable for drinking and irrigation purposes, with low concentrations of all parameters. However, in the high plain area, total hardness (TH), high total dissolved solids (TDS), and Cl⁻ and SO₄²⁻ concentrations limit the suitability of the groundwater for drinking purposes, while high EC and Na concentration makes it unsuitable for irrigation. These results aid in sustainable management of water resources in the study area, and provide a reference for the sustainable utilization of water resources and the rational exploitation of natural resources in other coal mining areas of the world.