Identifying and quantifying groundwater inflow to a stream using 220Rn and 222Rn as natural tracers

Abstract Study region Noseong Stream watershed in Nonsan, Chuncheongnam-do, South Korea. Study focus This study aims to identify and quantify groundwater inflow to a stream based on the spatial and temporal distributions of 220Rn and 222Rn activities in stream water and groundwater. Groundwater–stream water exchange fluxes were estimated on the basis of 222Rn mass balance approaches under losing and gaining stream conditions, and groundwater inflow type was identified using a spatial survey of 220Rn in stream water. New hydrological insights for the region The 222Rn activities at 20 stations along the stream during four sampling campaigns were higher at high altitudes than low altitudes, regardless of the season. At two sections, which appeared to be gaining systems, the groundwater inflow rates were estimated to be 6.5 × 102 and 4.0 × 102 m3 d–1. At another stream section, where groundwater inflow to the stream and stream water leakage into groundwater may alternatingly occur, the groundwater inflow and stream water leakage were 1.5 × 102 and 2.5 × 104 m3 d–1, respectively. A spatial survey of 220Rn along the stream indicates that groundwater may dominantly discharge to the stream water as point sources rather than diffuse seepage.