Hydrogeochemistry Assessment of Shallow Groundwater and Human Health Threats in the Northwestern Ordos Basin, China

Groundwater is the main sources of water supply for drinking purposes in the Ordos Basin in the northwestern part of China. In order to sustain and protect the quality of groundwater resources, shallow groundwater samples were collected and analyzed to identify the hydrogeochemical characteristics, and to evaluate health risk to human. Cluster analysis showed that the 134 groundwater samples were divided into three classes (i.e., class 1, class 2, class 3). The groundwater types are mostly characterized by SO4–Cl type and SO4 type, mixed HCO3 type. The primary natural mechanisms controlling the chemical compositions are water–rock interaction and evaporation–precipitation. The extremely high concentrations of sulfate could be caused by contamination from pyrite or from infiltration of sulfate from inorganic fertilizers or from wastewater discharges. Results of the assessment of the health risks for ingestion of Cl−, NO3−, F−, Cr, and As in drinking water indicated that the total health risks are beyond the US EPA acceptable level of 10−6 per year for consumption of groundwater sourced from all three cluster classes. The highest risks were for ingestion of arsenic and chromium in groundwater. The highest total risks to adults and children were 1.51 × 10−5 and 2.45 × 10−2 (class 1), 4.12 × 10−4 and 8.98 × 10−3 (class 2), 3.06 × 10−3 and 5.49 × 10−2 (class 3), respectively. The study showed that there is a high risk of health problems among the residents of the Ordos Basin in China that are ingesting contaminated drinking water, with the health risks to children higher than the risks to adults.