The International Information Center for Geotechnical Engineers

Soil Vapor Extrusion

 Predominant Processes in SVE

SVE is governed by four different processes, volatilization, advection, diffusion, and desorption (Sharma and Reddy 2004). Figure 2 shows a typical SVE setup and the processes that take place during the remediation technique.

  • Volatilization is the dominant process within the soil vapor extraction system because the contaminants are volatile substances that readily evaporate from the surface of particles.  Therefore, the contaminated vapor within the soil will be removed by the extraction wells. 
  • Advection is the transport of a substance through a medium, whether it be a fluid or air.  In the case of SVE it is the transport of contaminants through air.  The contaminants within the vadose zone move due to a negative pressure gradient within the soil caused by the vacuums applied to the extraction wells.  This negative pressure gradient causes the contaminated air to migrate towards the extraction wells.
  • Diffusion is a process where a substance will spread out or “diffuse” into the surrounding area.  Diffusion occurs due to a negative concentration gradient caused by the extraction wells, so the contaminants with the higher concentration will diffuse toward the wells where there is little to no concentration of contaminants.  Diffusion occurs until there is no concentraion gradient within the soil.
  • Desorption is the process by which a substance is removed from a surface.  Due to the applied vacuum, the soil-air is removed from the surface of the soil and moves throughout the void spaces of the soil particles towards the extraction wells because of a concentration gradient within the soil.

 

Figure 5

Figure 2. SVE Transport Processes (USACE, 2002)

 

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