We investigated sampling methods for measuring Rn-222 activity in groundwater to ensure the reliable collection of representative samples that reflect aquifer characteristics. In particular, we considered the effects of groundwater purging time and aeration during the water pumping process. Three different groundwater wells were investigated for the experiments, and Rn-222 activity in groundwater was measured using a liquid scintillation counter (Perkin Elmer, Wallac 1220 Quantulus). The constant Rn-222 activity was observed after approximately 15 minutes of groundwater purging. A decrease in Rn-222 activity was observed as the pump capacity increased, suggesting that the aeration effect was mitigated below a pump capacity of 3 L min-¹. Therefore, in field investigations where prolonged purging is not feasible, it is recommended to purge for at least 15 minutes with a pump capacity below approximately 3 L min-¹ to reduce purging time and minimize the aeration effect. This study is expected to serve as a valuable foundation for establishing guidelines for systematic groundwater sampling methods

Keywords: Groundwater sampling; Rn-222; Purging time; Aeration effect; Liquid scintillation counter