Isotopic and geochemical characteristics of groundwater in the Zagiin usnii khooloi, Southern Gobi region, Mongolia

Abstract:

In the Southern Gobi region, due to low rainfall and limited surface water, groundwater is the only source of water for domestic and industrial use. In the future, the “Zagiin usnii khooloi” groundwater reservoir will be used as a water supply for a large coal mining company operating in the region. In order to gain a better understanding of the groundwater’s ability to sustainably support the mining operation, major ions and stable isotopes in groundwater were analyzed in order to investigate groundwater sources and their associated recharge processes. The analyses were conducted in the laboratory of Geofluids Dynamics, Yonsei University.

A total of 64 water samples from a deep Cretaceous confined aquifer and a Quaternary shallow aquifer were collected in July and December 2019. The deep aquifer is classified as a NaCl type with high TDS. During the July 2019 sampling event, the shallow aquifer was characterized by Na-HCO₃ and Mg-HCO₃ water types, whereas SO₄ ion concentrations were found to be increased in the December 2019 round of sampling. The stable isotope analysis showed that groundwater in the deep aquifer was more isotopically depleted than the water in the shallow aquifer. The preliminary results of the stable isotope and geochemical characterizations in the study area indicate that the deep aquifer is not hydraulically connected with the shallow aquifer.