FORMATION CONDITIONS OF GROUNDWATER IN THE MEKONG DELTA (VIETNAM) BASED ON ISOTOPES RESEARCH OF OXYGEN AND HYDROGEN IN WATER

Abstract

The origin and formation of the groundwater in the Mekong Delta are the complex problem, which has not one solution nowadays. So the exploitation scheme still has many limitations. In the aquifers of the Mekong Delta there are both fresh water and mineralized water, which are very complex and heterogeneous in the distribution. The mineralized water has been considered to have sedimentagenous genesis (buried seawater), and freshwater has been believed to originate from infiltration of meteoric water. Studying of the stable isotopes of oxygen and hydrogen of the groundwater in the Mekong Delta has shown that the groundwater originates mainly from the infiltration of the meteoric water. In addition, a significant factor in the formation of groundwater in the Middle, Lower Pliocene and Miocene aquifer is the mixing of the meteoric and sea waters. Increasing in values of stable isotopes with growing depth of groundwater is related with that the recharging areas of Paleogene (deep) aquifers are distributed higher by absolute depths and farther from the coastline than recharging areas of Quaternary (shallow) aquifers. The results of the research can be used to optimize the scheme for the exploitation of the fresh groundwater, limiting the intrusion of sea water in the exploited groundwater in the Mekong Delta.