Study of Air Relative Permeability Evolution during Soils Decontamination by Soil Vapour Extraction

Soil vapour extraction (SVE), is the primary method used in the world to remove volatile organic compounds (VOCs) from unsaturated subsurface porous media. The objective of this work is to study the change of the soil air relative permeability during continuous venting and removal of contaminant from a polluted soil. Once the flow starts, the contaminants will volatilize and the volume of liquid phases (Non aqueous phase liquid NAPL and water) will decreases with time accordingly as long as the venting process is continuous. A correlation that describes the evolution of the relative air permeability as a function of the gas saturation degree has been established by fitting pneumatic tests data, conducted a small-scale laboratory pilot, to an analytical gas flow model. The experimental correlation were compared to models developed previously [1,2]. A significant difference between simulated breakthrough curves, which illustrate evolution of contaminant concentration in the extracted gas, based firstly on the relationship established experimentally and on the other hand on the two other correlations was observed. The difference between the three curves becomes more important when the PLNA initial saturation in soil is high. These results lead us to say that the evolution of air relative permeability according to the total liquids saturation degree should be determined experimentally. Inadequate characterization of this evolution may generate significant errors in removal rate and closer time estimates.