Hydrogeochemical characterization and suitability assessment of groundwater in an agro-pastoral area, Ordos Basin, NW China

Groundwater is vital to supply residents, livestock and agriculture in Daniudi gasfield area, which is a typical agro-pastoral area. To effectively protect and rationally utilize the groundwater, a hydrochemical investigation of 43 samples from this area was conducted. A hydrogeochemical assessment using a Piper diagram, correlation analysis, ratios of major ions, principle component analysis and saturation index calculations was carried out to detect the hydrochemical characteristics and evolution processes of the groundwater from a Quaternary aquifer (QA) and a Cretaceous aquifer (KA), and fuzzy synthetic evaluation and some water quality indices were applied to assess groundwater suitability for drinking and irrigation. According to the statistic summary, the average abundance of the major ions in groundwater from the QA and KA follows the order: HCO₃ ⁻ > SO₄ ²⁻ > Cl⁻ for anions and Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ for cations. There is evidence that the chemical composition of groundwater in the region has been influenced by human activities. The dominant hydrochemical facies of the groundwater is HCO₃–Ca type. Dissolution of carbonate and evaporite minerals and the weathering of silicate minerals are likely to be the sources of major ions in groundwater. Ion exchange is another significant factor affecting the groundwater constituents. Gibbs diagrams suggest that rock weathering is the control process of groundwater chemical composition. As to suitability of groundwater for drinking, single parameter comparison and fuzzy comprehensive evaluation reveal that most of the groundwater in the study area is suitable for drinking under ordinary condition. A US Salinity Laboratory diagram, Wilcox diagram and some irrigation indices indicate that more than 90 % of the groundwater samples are suitable for use in irrigated agriculture.