Study the Upper Pleistocene groundwater dynamic in the Nambo Plain for sustainable management of groundwater resources by isotope techniques

The isotope technique was used to study the groundwater dynamics of the Upper Pleistocene aquifer in the Nambo Plain, by which stable isotope (O-18, H-2) composition of groundwater samples was used to define the origin of groundwater and their tritium and C-14 content were used to determine groundwater age and predict the aquifer's recharge zone. The results show that the fresh groundwater in the study aquifer is of meteoric origin, while the saline groundwater is the result of mixing fresh groundwater with saline water of marine origin. The groundwater age of the study aquifer ranges from modern to about 29,000 years old; the spatial distribution of groundwater age shows that water in the study aquifer moves along two directions, such as from northwest to southeast and from northeast to southwest, with an average velocity of 7.7 m/year and 8.1 m/year, respectively. The study aquifer has a recharge zone in the northeast part of the Plain, and another one may be in Cambodian territory, outside of Vietnam.