Difference in Transport Behavior between Aliphatic and Aromatic Petroleum Vapors in Unsaturated Soil

Abstract

Unsteady state multicomponent vapor transport experiments in large (10.5 cm × 100 cm) columns packed with dry and wet soil and dry sand were used to evaluate the difference in transport behavior between aliphatic and aromatic petroleum vapors. The experimental data were analyzed using a modified diffusion equation accounting for vapor sorption and vapor partitioning into the soil moisture. Excellent agreement between the diffusion model and the experimental data was observed for all vapors studied in dry sand and dry soil and for aliphatic vapors in wet soil. However, a poor agreement was observed between the model and the aromatic vapors in wet soil. This was attributed to mass transfer limitation and violation of the local equilibrium assumption used to describe aromatic vapor partitioning into the soil moisture. Significant reduction in retardation factors for all vapors was observed in wet soil due to sorption competition by water molecules, but aromatic retardation factors were higher than the aliphatic ones, because of their high solubility and partitioning into the soil moisture.