Radon and Strontium Isotopes as tracers for quantifying mixing process of groundwater and surface water in riverside area

Interaction of surface water and groundwater has been studied for providing useful background information on the development of indirect open loop ground source heat pump (GSHP) at Han River Environmental Research Center (HRERC) in Korea. The natural radiogenic tracers, Radon-222, can be used as good indicator for calculating mixing ratio between groundwater and surface water as it has much higher concentration in groundwater than in surface water. In addition, the quantitative interpretation as mixing ratio of groundwater and surface water can be recognized based on the linear relationship of 87Sr/86Sr ratio and Sr concentration in water samples. Therefore, 18 groundwater wells and surface water were used for monitoring radon concentration, strontium concentration, and hydrogeochemical parameters for three times in 2016. The calculated mixing ratio using radon tracer indicated that Han River flow would have a considerable impact on the operation of GWHP in the study area because of high surface water ratio of 50.09 percent. The 87Sr/86Sr ratios of groundwater samples were from 0.7243 to 0.7584 whereas the ratio of surface water was from 0.7197 to 0.7282. The results of two end member mixing model using strontium tracer showed that the value of average groundwater ratio (50.11 percent) was similar to the results of radon tracer (50.09 percent). The mixing ratio results of radon tracer of each month also showed that it had linear relationship with the results of strontium tracer. The spatial distribution of mixing ratio using radon and strontium concentration was found to be affected by water level fluctuation by nearby dam activity, not by only nearby surface water. This study reveals that radon and strontium isotope can be used as an appropriate environmental tracer in examining the mixing processes in the riverside area.