Hydrochemistry and the Flow System of Selected Geothermal Groundwater in Korea

Hydrochemical and isotope study has been conducted for three years to understand the flow system and changes of geothermal groundwater at four sites in Korea, which covers one coastal site and three inland sites. At each site, surface water and shallow groundwater were also sampled and the analytical results were compared with those of geothermal groundwaters.  

The coastal geothermal groundwater show the Na/Cl ratio about 0.48, seven times higher EC values and heavier isotope values ( ¹⁸O to 2.98‰, δ²H to 18.3‰) than shallow groundwater, indicating directing impact of sea water into the geothermal system. However, in the inland sampling sites, all the geothermal groundwater, shallow groundwater and surface water have similar ⁸⁷Sr/⁸⁶Sr ratio each other, implying that hydrochemistry of the those waters were formed by basically same water-rock interactions. Using the NETPATH program with the corrected ¹⁴C data, the circulation time of rainfall to geothermal groundwater were estimated to be from 2,000 to 5,700 years at the sites. The deeper the wells, the older the ¹⁴C age of groundwater. Hydrochemistry of deep geothermal groundwater in inland sites appear to be similar, but became diversified along the flow paths to the shallow groundwater system. Accounting for the age of waters and their hydrochemistry, it seems that the infiltrated rainfall forms shallow groundwater with diversified composition, and takes long time to become geothermal groundwater with strong water-rock reactions.