Passive volatilization behaviour of gasoline in unsaturated soils

Gasoline behaviour in the unsaturated zone is difficult to predict as a number of soil factors, gasoline properties and environmental conditions will determine the eventual fate of a spill. These factors include the diffusive and convective processes that contribute to passive volatilization. To gain a better insight into passive volatilization and how it can impact the clean-up of a contaminated site, batch column experiments were completed. Three soils were tested at varying initial gasoline contents, water contents, and at room and sub-zero temperatures. The results indicate that immiscible phase movement to the surface is a significant contributor to passive volatilization. However, the immiscible phase movement ceases once the gasoline content has dropped below a threshold level. The driving force necessary for immiscible phase movement is maintained by gasoline precipitation at the soil surface. Higher soil water contents inhibited the volatilization of gasoline as water impacted both the diffusive and wicking movement of the gasoline. Sub-zero temperatures reduced volatilization and extended the time to cessation of wicking behaviour.