Field study of using naturally occurring radon to assess the dense non-aqueous phase liquid distribution in saturated zone

The concept of radon deficiency such as the ratios of radon concentrations to the maximum measured value of a sample batch was employed as the survey methodology for this study to investigate contamination sources in an industrial zone that was suspected of causing subsurface dense non-aqueous phase liquid (DNAPL) contamination. The results showed that radon concentrations in certain wells were significantly lower than that in uncontaminated regions. Radon concentrations in groundwater are influenced by the in situ bioremediation of vegetable oil, which causes abnormal reductions of the radon in groundwater because radon partitions into vegetable oil and results in more variable for the radon deficit method to showing the impacts of remediation. Six contaminated regions were identified by integrating radon concentration ratios (divided into low (L), middle (M), and high (H) levels) and DNAPL concentrations (divided into low (L) and high (H) levels). Contaminated regions in the LH, MH, and HH categories are located in the vicinity of the contamination source, and those in the HL category are located far from the source zone. The ML and LL categories indicate the involvement of unknown factors, and that additional analyses are required to uncover the facts that affect radon and DNAPL concentrations. -- Highlights: • Radon deficient can reveal potential hot spots for DNAPL contaminated sites. • Bioremediation injections interfere the measurement of radon in groundwater. • Six region types in a site are classified based on radon and DNAPL concentrations