Effect of NAPL mixture and alteration on ²²²Rn partitioning coefficients: Implications for NAPL subsurface...

Area of Science:

• Environmental Science
• Geochemistry
• Environmental Engineering

Background:

• Soils and groundwater are frequently contaminated by Non-Aqueous Phase Liquids (NAPLs), posing environmental risks.
• Traditional NAPL quantification methods are complex and costly.
• Using natural soil gas, such as radon (²²²Rn), offers a potentially simpler and cheaper alternative for NAPL detection.

Purpose of the Study:

• To investigate the impact of NAPL degradation on radon partitioning coefficients (K_n-w).
• To assess how evaporation and UV degradation affect K_n-w for commercial diesel fuel and gasoline.
• To understand the implications for radon-based NAPL subsurface quantification.

Main Methods:

• Conducted batch experiments to determine radon partitioning coefficients (K_n-w) for fresh and degraded NAPLs.
• Utilized Gas Chromatography-Mass Spectrometry (GCMS) for molecular investigation of NAPL degradation.
• Analyzed commercial diesel fuel and gasoline under simulated evaporation and UV-degradation conditions.

Main Results:

• Fresh diesel fuel showed a K_n-w of 60.7 ± 6.1, while fresh gasoline had a K_n-w of 37.4 ± 5.6.
• Degraded diesel fuel exhibited altered K_n-w values: 74.8 ± 7.5 (UV) and 25.1 ± 2.5 (evaporated).
• Gasoline showed no significant K_n-w variation after degradation, with only minor removal of volatile compounds observed via GCMS.

Conclusions:

• NAPL degradation significantly affects radon partitioning coefficients for diesel fuel, influencing ²²²Rn-based quantification.
• Gasoline's K_n-w remained largely unaffected by the tested degradation pathways.
• Accurate interpretation of ²²²Rn activity for subsurface NAPL quantification requires consideration of NAPL degradation state.