Passive volatilization behaviour of gasoline in unsaturated soils

Gasoline behaviour in the unsaturated zone is difficult to predict as a num ber 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 gai n a better insight into passive volatilization and how it can impact the cl ean-up of a contaminated site, batch column experiments were completed. Thr ee 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 vola tilization. However, the immiscible phase movement ceases once the gasoline content has dropped below a threshold level. The driving force necessary f or immiscible phase movement is maintained by gasoline precipitation at the soil surface. Higher soil water contents inhibited the volatilization of g asoline as water impacted both the diffusive and wicking movement of the ga soline. Sub-zero temperatures reduced volatilization and extended the time to cessation of wicking behaviour. (C) 1999 Elsevier Science B.V. All right s reserved.