Dense non-aqueous phase liquids (DNAPLs) pose significant threats to the ecosystem and human health due to their persistence and migration in groundwater. This study evaluates the application of radon as a natural tracer for identifying DNAPL distribution within a bedrock aquifer, where traditional radon deficiency principles may be compromised by factors such as high permeability fractures. For this, two push-pull tests were conducted. The results from the inter-well test highlighted that radon behavior was dominated by mixing processes with background water, indicating that the radon tracer can act similarly to the conservative tracer without contamination of DNAPL. Conversely, the single-well test indicated that radon concentrations were influenced by phase partitioning with TCE within a certain radial range, suggesting the presence of entrapped TCE within this particular area. While this heterogeneous existence of TCE was interpreted to induce the non-conventional breakthrough curve (BTC) patterns, heterogeneity of the flow field was also determined to be a potential reason. Overall, the findings confirm that radon can be effectively utilized as a tracer for monitoring DNAPL distribution within bedrock aquifers, considering the main influential physical processes, including phase partitioning with TCE or mixing processes with other water bodies.

Keywords: Radon, Dense non-aqueous phase liquids, Single-well push-pull test, Inter-well push-pull test, Bedrock aquifer