Distribution and evolution of high-fluoride shallow groundwater in Datong Basin, China

The occurrence and controlling factors of high fluoride concentrations in shallow ground waters of the Datong basin, northern China, were investigated. The results showed that high F- groundwater is mainly distributed in the transitional zone between the pluvial plain and the alluvial-lacustrine plain in the Datong Basin. The F-concentration was up to 4.5 mg/L, with an average value of 1.33 mg/L. Along the regional flow path, from the mountain front to the central part of Basin, F-concentration increases gradually. The high F-groundwater are characterized by high pH, low content of Ca2+, high contents of HCO3- and Na+, and moderate TDS content. Hydrolysis of F-bearing minerals is the dominant processes affecting F- levels, and less important is evaporation-condensation in the groundwater. The process of evaporation to a certain degree is favorable for fluoride enrichment in groundwater, but excessive evaporation hinders further increase in F-concentration.