The EPA’s Citizen’s Guide to Cleanup Technologies Series 3: Soil Vapor Extraction and Air Sparging

May 10, 2017

Environmental Enlightenment #202

See our Newsletter, Environmental Enlightenment #200, for introduction to one highly valuable, plainly written series of Citizen’s Guides published by the EPA at http://www.clu-in.org/products/citguide

With this issue, we introduce the EPA’s Citizen’s Guide to Soil Vapor Extraction and Air Sparging. You can reach it through the hyperlink under the blue header below.

https://clu-in.org/download/Citizens/a_citizens_guide_to_soil_vapor_extraction_and_air_sparging.pdf

Sparging is the action of bubbling gas or air through liquid. (Wikipedia)

water droplets on glass panel

Vapors consist of molecules that move off from a substance.

 

All what matter is, is a balled-up conglomeration of motions and when enough energy is present, certain motions detach from the “mother ship” and become “vapor.”

Illustration © Rod Nave, HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

In a greater or lesser degree, all substances give off vapors: water spilled on the floor disappears after a time; it has evaporated.

Certain liquids evaporate faster than other liquids.

Acetone evaporates fast, really fast.

Lead evaporates slow, very slow.

I remember a guided tour back in 1978 at the Yale campus in New Haven, Connecticut. Our guide pointed to parts of a leaded roof that evaporated over the ages.

Photo credit: Kevin Rosseel, Morguefile.com

If you spill a liquid in a closed room, after a time its vapors will fill up the room and the puddle will stop evaporating. 

Illustration © Rod Nave, HyperPhysics http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

The same happens to liquids that penetrate the subsurface soil; they give off vapors that permeate and fill up the pores of the soil.

Comparative pore space: 
Left: soil with large pore space.
Right: Compacted soil lacking large pore space.

Illustration courtesy of Colorado Master Gardener Program, Colorado State University Extension
(http://www.cmg.colostate.edu/gardennotes/213.html)

If you want to dry up moisture, you blow air upon it.

The air stream captures the molecules that the substance gives off and carries them away, thus enabling the substance to release additional vapor.

In a similar way, we use vacuum to induce airflow through the soil. We want it done by vacuum rather than pressure because we want the captured, toxic vapor to be drawn into our suction machines, which feed it to the vapor treatment part of the operation where the vapor is destroyed or captured for treatment off site.

This operation is called soil vapor extraction or SVE.

By its very nature it can work only on the soil that is above the water table.

Sparging is used to remove volatile contaminants that have lodged in the saturated soil under the water table.

Air is bubbled under pressure, and the bubbles search ways to rise in the aquifer. The tighter the aquifer (for example, clay), the harder it is for the bubbles to move. Thus, sparging works best with loose aquifers. Various combinations of sand, gravel, silt, and clay make for loose aquifers. Solid layers of clay and silt make aquifers tight.

Go to: http://www.clu-in.org/download/Citizens/a_citizens_guide_to_soil_vapor_extraction_and_air_sparging.pdf
for the rest.

It is easy to understand and… interesting!

Image courtesy of NEXT Environmental Inc. (http://www.nextenviro.com)

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