Major Ion Chemistry of Shallow Groundwater in the Dongsheng Coalfield, Ordos Basin, China

A hydrogeochemical study was conducted in the Dongsheng Coalfield, Ordos Basin, China, to identify the mechanisms responsible for the chemical compositions of the shallow groundwater and to document water quality with respect to agricultural and drinking supply standards, prior to mining. Tri-linear diagrams, principal component analysis, and correlation analysis were used to reveal the hydrogeochemical characteristics of the shallow groundwater, and the potential water-rock interactions. In general, the major cations and anions were present at low concentrations, but were relatively higher around Jiushenggong than elsewhere in the study area. Groundwater around Jiushenggong has a long residence time and is also subject to extensive evapotranspiration. The dominant hydrochemical facies are HCO3-Ca, HCO3-Na, and mixed HCO3-Ca center dot Na center dot Mg types. Increases in major ion concentrations along the flow path, including Na, Cl, and SO4, coincide with increases in total dissolved solids. The predominant mechanism controlling groundwater chemistry proved to be the dissolution of carbonates, gypsum, and halite. Cation exchange and mixing with local recharge water are also important factors. The shallow groundwater quality in the study area is suitable for agricultural and drinking purposes.