Application of single-well push-drift-pull tests using dual tracers (SF 6 and salt) for designing CO 2 leakage monitoring network at the environmental impact test site in Korea

A single-well push-drift-pull tracer test using two different tracers (SF6 and salt) was performed at the Environmental Impact Test (EIT) site to determine suitable locations for monitoring wells and arrange them prior to artificial CO2 injection and leak tests. Local-scale estimates of hydraulic properties (linear groundwater velocity and effective porosity) were obtained at the study site by the tracer test with two tracers. The mass recovery percentage of the volatile tracer (SF6) was lower than that of the non-volatile tracer (salt) and increased drift time may make degassing of SF6 intensified. The CO2 leakage monitoring results for both unsaturated and saturated zones suggest that the CO2 monitoring points should be located near points at which a high concentration gradient is expected. Based on the estimated hydraulic properties and tracer mass recovery rates, an optimal CO2 monitoring network including boreholes for monitoring the unsaturated zone was constructed at the study site.