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Air Sparge & Vacuum Extraction

Vacuum extraction draws contaminants from the soil in vapour form by applying a vacuum through a system of underground wells.

Vacuum extraction can be used to target volatile contamination in the unsaturated zone. The process works by applying a vacuum through either vertical or horizontal wells installed within the area of impact. Vapours within the ‘pore-space’ are recovered, which in turn draws volatile contamination adsorbed into soil out into the ‘flushed clean’ pore-space or promotes its biodegradation as a consequence of drawing in oxygen laden air. It should however be noted that both of the processes can be very slow (rate limiting), particularly where the impacted geology has a high organic content or where the original spillage occurred a long time ago.

The air sparging component is used specifically to target dissolved phase volatile contamination within the saturated zone. Compressed air, injected through specially designed wells that are screened within the aquifer, bubble to the surface. A percentage of the volatile contamination dissolved in the water will transfer into the air bubbles where they are transported to the surface for recovery by the vacuum extraction system. Like the vacuum extraction system the addition of air also helps stimulate indigenous aerobic bacteria, biodegrading some of the encountered contamination.

When designing an air sparging system due consideration needs to be given to the permeability of the geology (it has limited effectiveness in low permeability formations), the level of contamination (not recommended for grossly contaminated zones or where NAPL is present), depth of contamination (the mass transfer of volatiles into the sparge bubbles is a two way process hence you could smear contamination across the aquifer) and the type of contaminant.

If designed properly an Air Sparge / Vacuum Extraction (AS/VX) solution could be cost effective. Typically extracted vapours are treated through GAC filters prior to discharge to atmosphere. Additional separation plant may be required to remove water entrained within the extracted vapour and air. Churngold can provide all necessary assistance from design through to the implementation of an AS/VX system.