Abstract:

Not only high As groundwater but also high F- groundwater have been found in the Hetao basin of Inner Mongolia. Although much work has been done on high As groundwater, little is known about the distribution and genesis of high F- groundwater. Based on reviewing of previous data and hydrogeological setting, 406 groundwater samples were collected and analyzed from the Hetao Basin of Inner Mongolia. Mineral dissolution and precipitation, evaporation, competitive adsorption and desorption, and cation exchange were integrated to discuss the major mechanisms controlling the enrichment of groundwater fluoride in the plain and the piedmont areas in Hetao Basin with different hydrogeological conditions. Results show that over 59% of groundwater samples have fluoride concentration above the Chinas drinking water standards of 1.0 mg/L. Relatively more groundwater samples having fluoride concentrations greater than 1.0 mg/L in the piedmont area which is higher than those in the plain area. Highfluoride groundwater usually show high concentrations of Na+ and alkalinity and low concentration of Ca2+. In the flat plain, groundwater are normally higher in pH, HCO-3, δ18O, δD and TDS, and lower in Ca2+ and NO-3 than those in the piedmont area. The fluorite dissolution and calcite precipitation are the major factors controlling fluoride enrichment in groundwater at the piedmont area, while evaporation, cation exchange, competitive adsorption between OH-, HCO-3 and F- become the main controlling factors in groundwaters of the flat plain.

Key words: Hetao basin, hydrogeochemistry, fluoride groundwater, distribution characteristics, genesis