ANALYSIS OF RECHARGE SOURCES AND HYDROGEOCHEMICAL PROPERTIES OF GROUNDWATER IN TAMUSU, ALXA, INNER MONGOLIA

Tamusu, located in Alex, Inner Monglia, northwestern China, is one of the preselected area for high-level radioactive waste geologic disposal of China. Carrying out hydrogeological assessment at potential disposal sites of interest is particularly important for getting scientific results of suitability. In particular, knowing about recharge sources and evolution processes of groundwater will help to further understand the formation and renewal of groundwater. Combining the hydrogeological conditions in Tamusu area, using hydrogeochemical and isotopic techniques to get the results of 26 specimens which were collected from the study area. The results show that groundwater in the study area mainly originated from local precipitation because there was similar isotopic characteristics between them. It is also consistent with the hydrogeological conditions in the study area. The typical feature of groundwater is high salinity and the TDS average value is about 2.9 g·L^-1. Meanwhile, almost all samples were Na⁺-Cl^- type. This is a common phenomenon in arid regions. Moreover, two chloroalkaline indices of groundwater are positive and there are good linear relationship between Mg²⁺+Ca²⁺-HCO₃^--SO₄^2- and Na⁺+K⁺-Cl^- with a slope of-1. This indicates that ion exchange is a significant geochemical process for controlling the composition of groundwater. The groundwater in study area is not fit to drink due to high salinity and the age of deep groundwater older than 5000 a because of weak renewal. This cognition provides crucial hydrogeological evidences for site selection and evaluation in the area.