Citizen's Guide to Soi
" - -Ion and Air.~^
What Are Soil Vapor Extraction And
Air Sparging?
Both soil vapor extraction, or "SVE," and air sparging
extract (remove) contaminant vapors from below
ground for treatment above ground. Vapors are the
gases that form when chemicals evaporate. SVE
extracts vapors from the soil above the water table by
applying a vacuum to pull the vapors out. Air sparging,
on the other hand, pumps air underground to help
extract vapors from groundwater and wet soil found
beneath the water table. The addition of air makes the
chemicals evaporate faster, which makes them easier
to extract with another technology, such as SVE.
Both methods are used for chemicals that evaporate
easily—like those found in solvents and gasoline. These
chemicals are known as "volatile organic compounds,"
or "VOCs."
How Do They Work?
Extraction:
SVE involves drilling one or more extraction wells into
the contaminated soil to a depth above the water table,
which must be deeper than 3 feet below the ground
surface. Attached to the wells is equipment (such as
a blower or vacuum pump) that creates a vacuum.
The vacuum pulls air and vapors through the soil
and up the well to the ground surface for treatment.
Vapor Treatment
Building -\ | Clea
Illustration of a combined air sparging and SVE system.
Sometimes the ground must be paved or covered with
a tarp to make sure that the vacuum does not pull air
from above into the system. Pulling in clean air would
reduce the efficiency of the cleanup. The cover also
prevents any vapors from escaping from the ground to
the air above.
Air sparging involves drilling one or more injection
wells into the groundwater-soaked soil below the
water table. An air compressor at the surface pumps
air underground through the wells. As air bubbles
through the groundwater, it carries contaminant vapors
upward into the soil above the water table. The mixture
of air and vapors is then pulled out of the ground for
treatment using SVE.
Treatment:
Extracted air and contaminant vapors, sometimes
referred to as "off-gases," are treated to remove any
harmful levels of contaminants. The off-gases are first
piped from the extraction wells to an air-water separator
to remove moisture, which interferes with treatment.
The vapors are then separated from the air, usually by
pumping them through containers of activated carbon.
The chemicals are captured by the carbon while clean
air exits to the atmosphere. (See A Citizen's Guide to
Activated Carbon Treatment [EPA 542-12-001.]).
Filter materials other than activated carbon may be
used. In a process called "biofiltration," tiny microbes
(bacteria) are added to break down the vapors into
gases, such as carbon dioxide and water vapor.
Another option is to destroy vapors by heating them to
high temperatures.
How Long Will They Take?
Cleaning up a site using SVE or air sparging may take
several years. The actual cleanup time depends on
several factors. For example, cleanup may take longer
where:
Contaminant concentrations are high.
The contaminated area is large or deep.
• The soil is dense or moist, which slows the
movement of vapors.
These factors vary from site to site.
-------
Are SVE And Air Sparging Safe?
When properly designed and operated, SVE and air sparging pose little
risk to site workers or the community. Treatment of the vapors involves no
harmful chemicals that must be transported to the site. Chemical vapors
are contained from extraction to treatment so they cannot be accidentally
inhaled by anyone nearby. Only clean air that meets air quality standards
is released. The air released to the atmosphere following treatment
may be sampled to make sure all harmful vapors have been removed
or destroyed.
How Might It Affect Me?
Area neighborhoods may experience some increased truck traffic as the
equipment for SVE or air sparging is delivered and later removed. Installation
of the systems involves the use of drilling rigs and sometimes other heavy
machinery to install wells, blowers, and treatment equipment. Sheds or
larger buildings may be built to house the treatment systems, keeping any
noise to a minimum. Workers will visit these systems regularly to ensure they
are working.
Why Use Soil Vapor Extraction And Air Sparging?
SVE and air sparging are efficient ways to remove VOCs above and below the
water table. Both methods can help clean up contamination under buildings,
and cause little disruption to nearby activities when in full operation. SVE and
air sparging are often used together. SVE and air sparging are being used
or have been selected for use at approximately 285 and 80 Superfund sites,
respectively.
Pipes transport vapors from the
underground SVE extraction well
to treatment.
Above-ground treatment system includes two tanks of
activated carbon.
Example
Both SVE and air sparging are
being used to clean up several
acres of contaminated soil and
groundwater at the Vienna PCE
Superfund site in West Virginia.
Two dry cleaning facilities
contaminated the area with PCE
(also known as perchloroethene
or "perc"), a solvent used to clean
clothing, forcing the shutdown of
the town's drinking water wells.
In 2005, construction of the
cleanup systems was completed
and included 74 air sparging
wells, 34 extraction wells,
and four treatment buildings.
The off-gases are piped to an
air-water separator, followed by
containers of activated carbon
for treatment. By 2010, 1,618
pounds of PCE had been
removed and PCE concentra-
tions had decreased by as much
as 99% in some wells. EPA will
continue to operate the systems
and monitor PCE levels until
cleanup objectives have been
reached throughout the site.
For More Information
For more information on this
and other technologies in the
Citizen's Guide Series, contact:
U.S. EPA
Technology Innovation &
Field Services Division
Technology Assessment Branch
(703)603-9910
Or visit:
www.cluin.org/sve
www.cluin.org/airsparging
NOTE: This fact sheet is intended solely as general information to the public. It is not intended, nor can it be relied upon, to create any
rights enforceable by any party in litigation with the United States, or to endorse the use of products or services provided by specific
vendors. The Agency also reserves the right to change this fact sheet at any time without public notice.
United States
Environmental Protection
Agency
Office of Solid Waste and
Emergency Response
(5102G)
EPA 542-F-12-018
September 2012
www.epa.gov/superfund/sites
www.cluin.org
------- |