Use of isotope techniques to evaluate the recharged ability of the upper pleistocene aquifer in the nambo plain

In the Nambo Plain, the monitoring data on dynamics and quality of groundwater has shown declining signs in quantity and quality both in the existing groundwater aquifers, and the exploitation of groundwater in recent time is believed to be a cause of this decline. That shows the need for further research, especially on the modern recharge ability of the existing groundwater aquifers, to re-evaluate the groundwater potential of the region. For that purpose, isotope techniques are applied to evaluate the recharge ability of the upper Pleistocene aquifer (qp3), an important source of water supply in rural areas in the Nambo Plain under the framework of a project conducted by the Center for Nuclear Technologies in 2020-2021. In this study, water samples including groundwater, river water and rainwater were collected and analyzed for stable isotope composition (²H, ¹⁸O), tritium (³H), radiocarbon (¹⁴C) and major hydro-chemical parameters. Data on stable isotope composition in groundwater are used to define the origin of groundwater while tritium and ¹⁴C content are used to determine groundwater age and to predict the aquifer's recharge zone; and in combining with the stable isotope composition and tritium content of river water to evaluate the dynamic relationship between river water and groundwater. So far, the obtained results show that: i) Groundwater in the study aquifer is originated from meteorological water and formed at different stages. ii) The high ³H and ¹⁴C content in some groundwater samples indicate that the aquifer has modern rainwater infiltrated as a recharge source. iii) The similarity of stable isotope composition in the Vam Co river water and groundwater adjacent to the river shows that there is a hydraulic relationship between them. This is an important basis for assessing the recharge ability to the qp3 aquifer of the Vam Co river water. This research is still ongoing. (author)