Chemical Evolution of Groundwater in the Tacheng Basin of Xinjiang in the Process of Urbanization

With the development of the local economy, the volume of groundwater production has increased continuously in the past decades in the Tacheng Basin of the Xinjiang Uygur Automous Region. Previous studies have not provided a clear pattern of the chemical composition evolution of groundwater and its driving force in this basin, which makes the future development and utilization of groundwater riskier. This study carried out systematic sampling and analysis of groundwater chemistry in this basin, and the chemical evolution of groundwater in the basin was analyzed by comparison with historical hydrochemical data. The results show that Ca2+ and Na+ are the main cations in the groundwater, HCO3-, SO42- are the main anions in the groundwater, and freshwater is widely distributed. The chemical types of groundwater changed from HCO3-Ca and HCO3·SO4-Ca·Mg in the source zone in front of the mountains to SO4·HCO3-Na·Ca type in the plain area. In comparison with the hydrochemical data of 1979, HCO3 and SO4·HCO3 type groundwater increased significantly. SO4 and Cl type groundwater with high total dissolved solids decreased significantly. However, the Cl- and SO42- concentration and total hardness in the groundwater around the cities and towns increased. Aquifer material and the change of flowing field are the two controlling factors of groundwater chemical change, but the leakage of waste water from city drainage channels also affects the groundwater chemistry drastically.