The use of radon (Rn-222) and volatile organic compounds in monitoring soil gas to localize NAPL contamination at a gas station in Rio Claro, São Paulo State, Brazil

• 222Rn in soil gases.
• Correlation between 222Rn and VOCs.
• Useful method as a preliminary fingerprint of a contaminated area.

This study focuses on the presence of radon (222Rn) and volatile organic compounds (VOCs) in soil gases at a gas station located in the city of Rio Claro, São Paulo, Brazil, where a fossil fuel leak occurred. The spatial distribution results show a correlation between 222Rn and VOCs, consistent with the fact that radon gas has a greater chemical affinity with organic phases than with water. This finding demonstrates that the presence of a residual hydrocarbon phase in an aquifer can retain radon, leading to a reduced radon content in the soil gas. The data in this study confirm the results of previous investigations, in which the method used in this study provided a preliminary fingerprint of a contaminated area. Furthermore, the data analysis time is brief, and only simple equipment is required.