The naturally occurring radioisotope 222 Rn was used as a partitioning tracer to evaluate the presence and amount of a non-aqueous phase liquid (NAPL) in an aquifer. The batch experiment results of a diesel contaminated soil showed that the emanation rate of 222 Rn decreased to 31%, relative to a background rate. Batch experiment results of water contaminated by gasoline, diesel, PCE and TCE were similar. A field study to examine TCE contamination was conducted using 54 groundwater samples in Wonju city, Republic of Korea. Estimates of TCE contamination ranged from <0.001mg/L to 14.3mg/L, and 222 Rn concentrations ranged from 1.89Bq/L to 444. Results of 222 Rn analysis showed that TCE contamination was mainly restricted to an asphalt laboratory area and that the 222 Rn values of a NAPL-contaminated aquifer were correlated with TCE analytical results.