Geochemical properties of groundwater affected by open loop geothermal heat pump systems in Korea

Abstract

This study was performed to examine the chemical and isotopic compositions of groundwater used in open loop GHP systems and natural groundwater around the open loop GHP systems and to evaluate the influence of open loop GHP systems’ operation on groundwater chemistry in Korea. The water temperature of groundwater used in open loop GHP systems ranged from 6.0 to 37.1°C and decreased by 6.7 to 11.6°C compared with that of natural groundwater around the open loop GHP systems. The pH, EC, Eh, Fe2+, and Mn2+ of the groundwater were not significantly affected by open loop GHP systems’ operation. The groundwaters used in open loop GHP systems showed various water types, such as Ca-HCO3, Ca-Cl, Ca-SO4, and Na-HCO3· Although HCO3 - and Cl- concentrations were slightly influenced by open loop GHP systems at some sites, the groundwater chemistry used in the open loop GHP systems did not significantly change at most sites. In addition, carbonate and silica minerals and minerals containing Mn were in undersaturated condition, which indicates that the precipitation of these minerals will not occur. However, some minerals containing Fe, such as Fe(OH)3, goethite, and hematite can be precipitated as scale within these system. In the open loop GHP systems selected in this study, the influence of open loop GHP systems on groundwater chemistry is not revealed sufficiently because of short-term monitoring of groundwater chemistry. However, integrated long-term monitoring is necessary to evaluate influence of open loop GHP systems on groundwater chemistry and to improve our understanding of the environmental impacts related to these systems.