I United States
.: Environmental Protection Agency
Office of Solid Waste and
Emergency Response (5203P)
EPA 542-F-l 0-007
March 2010
Green Remediation Best Management Practices:
Soil Vapor Extraction & Air Sparging
Office of Superfund Remediation and Technology Innovation
Quick Reference Fact Sheet
The U.S. Environmental Protection Agency (EPA) Principles for
Greener Cleanups outlines the Agency's policy for evaluating
and minimizing the environmental "footprint" of activities
undertaken when cleaning up a contaminated site.1 Use of
the best management practices (BMPs) recommended in
EPA's series of green remediation fact sheets can help project
managers and other stakeholders apply the principles on a
routine basis, while maintaining the cleanup objectives,
ensuring protectiveness of a remedy, and improving its
environmental outcome.2
Overview
Historically, approximately one-quarter of Superfund
source control projects have involved soil vapor extraction
(SVE) to remove volatile organic compounds (VOCs)
sorbed to soil in the unsaturated (vadose) zone. Air is
extracted from, and sometimes injected into, the vadose
zone to strip VOCs from the soil and transport the vapors
to ex situ treatment systems for VOC destruction or
recovery. SVE generally is used to:
Remove a VOC source by controlling and diverting
vapor migration from the source area(s) toward a point
of compliance, and
Remove vapors stripped from VOC-contaminated soil
by other soil treatment methods such as electrical
resistance heating at sites where the soil or
contaminants are not amenable to SVE treatment alone.
Air sparging (AS) involves injection of air into
contaminated groundwater to drive volatile and
semivolatile contaminants into the overlying vadose zone
through volatilization. SVE is commonly implemented in
conjunction with air sparging to remove the generated
vapor-phase contamination from the vadose zone.
In many cases, introduction of
groundwater and vadose zone
aerobic biodegradation of
contaminants below and above
the water table. Technologies
such as bioventing or
biosparging use active or
passive air exchange processes
similar to those used in SVE
and AS but focus on stimulating
natural biodegradation pro-
cesses and removing con-
taminant mass through vapor
extraction. Information about
air to contaminated
soils also enhances
SVE and air sparging
rely on air exchange
between the ground
surface and
subsurface to volatilize
contaminants, while
similar air-based
technologies promote
biodegradation of
contaminants by
microbial populations.
minimizing environmental footprints of these and other
biological technologies is provided in a green remediation
fact sheet specific to bioremediation.3a
Many opportunities exist for reducing the footprints of SVE
and AS implementation, which can: incur high rates of
electricity and fuel consumption due to long-term opera-
tion and maintenance (O&M); release contaminant
vapors through vertical short circuiting or incomplete
treatment of offgases; and require offsite disposal of
investigation and remedy construction wastes.
A Sampling of Electricity Consumed
by SVE Components over Three Years
Vacuum blower
Off-gas treatment system
Data monitoring and processing
Aboveground treatment structure
1 08,000 kWh
90,000 kWh
33,000 kWh
1 ,800 kWh
Total electricity consumption: 232,800 kWh
Electricity consumption by typical SVE equipment operating
for three years (excluding system design and construction)
could emit 184 tons of carbon dioxide (based on the average
U.S. fuel mix), which is equivalent to the electricity used by
nearly 22 homes over one year.
[http://www.epa.gov/RDEE/energy-resources/calculator.html]
A green cleanup involving SVE or AS will:
Reduce total energy use and increase renewable energy
use
Reduce air pollutants and greenhouse gas (GHG)
emissions
Reduce water use and
negative impacts on
water resources
Improve materials
management and waste
reduction efforts, and
Enhance land
management and
ecosystem protection.
Materials
& Waste
Energy
Core
Land & Elements
Ecosystems
Air
Water
Designing an SVE or AS System
Green remediation strategies for implementing SVE and
AS rely on early development of a conceptual site model
(CSM) that is refined as remedial activities progress. The
CSM provides a tool to support selection of green
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remediation options, supply field data for decision-
making, establish short- and long-term decision points,
and document the changes in site conditions over time.
Soil-vapor flow models coupled with thorough delineation
of source areas and vapor-phase plumes help optimize
well locations and screen depths. The footprints of field
data acquisition can be reduced through methods such as
using field test kits wherever possible for soil sampling.
Other best practices are described in a companion fact
sheet specific to site investigations.311
Optimizing the initial design of a vapor treatment system
can result in efficient use of resources and placement of
environmental safeguards.4 Project managers can reduce
energy consumption and related air emissions while
conserving other natural resources through BMPs such as:
Selecting vacuum pumps and blowers (including
multiple low-flow blowers) that accommodate changes
in operating requirements as treatment progresses
Using piping of sufficient diameter to minimize pressure
drops and resulting need for additional energy to
operate blowers
Using variable frequency drive motors to automatically
adjust energy use to meet system demand
Examining feasibility of using pulsed rather than
continuous air exchange processes, which can also
facilitate extraction of higher concentrations of
contaminants
Considering barometric pumping, which can use
barometric pressure differences to enhance air
throughput if adequate response lag exists between the
subsurface and atmosphere
Minimizing the size of the above-ground treatment
system and equipment housing and using energy-
efficient design elements such as passive lighting and
exterior shading, to minimize heating and cooling needs
Considering feasibility of increasing the number of AS
venting wells to decrease the applied flow, in light of
potential energy and materials tradeoffs associated with
additional well construction and operations
Planning for co-treatment of SVE vapors with offgases
from other treatment systems, when concentrations
allow, to gain efficiencies through economy of scale
Establishing decision points triggering a change in the
vapor treatment approach, such as switching from
thermal oxidation to granular activated carbon (GAC)
media; effective evaluation of alternate methods will
consider tradeoffs such as potential increases in
material consumption or waste generation, and
Establishing decision points that could warrant transition
from SVE to an alternate technology such as
bioremediation.
Project managers can also identify processes in which
renewable energy resources can be used as a power
source for air transfer, vapor treatment, and field
activities. Solar energy could be used, for example, to
provide the energy needed for separating oxygen from
ambient air when introduction of pure oxygen rather than
air is warranted for AS without SVE.
Profile: Former Ferdula Landfill
Ferdula, New York
* Designed an innovative SVE system to vacuum landfill gas
through exclusive use of wind energy
Installed a single windmill to provide direct power for the
vapor extraction wells and equipment for GAC treatment of
extracted vapor
* Confined all extraction and treatment equipment in a 150-
foot2 building located next to the windmill
* Used a pulsed vacuum process that optimized treatment
rates while allowing for full off-grid operations and
intermittent wind conditions
Optimized windmill design through use of aluminum
blades and a steel roller (instead of conventional steel
blades and bronze roller bearings) to improve performance
at wind speeds below 5 mph
Continuously monitored system operations through use of
a remote data collection system
Extracted nearly 1,600 pounds of total VOC mass to date,
over 7 years of operations
* Expended $14,000 for wind system installation at project
startup but avoiding $15,000 in annual electricity expenses
Use of horizontal vapor extraction wells can help minimize
upwelling caused by vacuum extraction in areas of
shallow groundwater and may improve overall efficiency
of air extraction. In cases where groundwater pumping is
needed to sufficiently depress the water table and prevent
upwelling, groundwater may be reinjected downgradient
of the treatment system to recharge the aquifer or, if
needed, treated above ground and then reinjected.
An onsite pilot test is recommended to:
Assure suitable sizing of equipment to be used in
adding or withdrawing air to or from the subsurface,
which will optimize energy use
Determine the minimum air flow rate that can meet the
cleanup objectives and schedule while minimizing
energy consumption
Evaluate the efficacy of air/vapor treatment, to identify
any opportunity for reduced material use or waste
generation, and
Establish a project baseline on information such as
electricity and water consumption, volumes of material
purchases, and offsite disposal volumes, which can be
used to identify, implement, and measure continuous
improvements to an operating system and identify
opportunities for modifications resulting in major
efficiency gains.
Generation of SVE and AS material waste and wastewater
relates primarily to ex situ treatment of vapors. Roughly
70% of Superfund SVE systems have used GAC treatment
and approximately 25% have used thermal or catalytic
oxidation. Wastes potentially needing offsite treatment and
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disposal include spent non-regenerable carbon canisters
or liquid condensate from air/water separators. Treatment
designs can include plans to:
Treat condensate in onsite systems where contaminant
types and concentrations permit
Recycle condenser water as supplemental cooling water
where concentrations permit
Reclaim uncontaminated pumped water and treated
groundwater for onsite use such as dust control,
vegetation irrigation, or process input for other
treatment systems, or
Avoid or minimize dewatering when lowering of the
water table is unneeded to treat the smear zone or
otherwise unnecessary, by reducing the applied vacuum
or installing additional extraction vents.
Design options for reducing the footprint of SVE or AS
also may involve system integration with other cleanup
technologies and evaluation of associated environmental
tradeoffs. Heat application through electrical resistance
heating or steam injections, for example, can mobilize
contaminants for subsequent capture by an SVE system.
This integrated approach may reduce treatment duration
but is likely to increase the remedial system's net energy
demand. Similarly, an SVE system design could
incorporate dual phase extraction technology to more
efficiently remediate capillary fringe areas consisting of
low permeability soil but at the expense of additional
energy input.
Efficiencies also can be gained through acquisition of green
goods and services. Green remediation tools in EPA's Green
Response and Remedial Action Contracting and
Administrative Toolkit Include sample contract language and
reporting structures for key issues such as energy use.5
Constructing an SVE or AS System
A significant portion of the environmental footprint left by
construction of an SVE system involves well installation.
The greatest opportunities for reducing this footprint
contribution relate to gaining fuel efficiencies, reducing
drilling waste, and minimizing land and ecosystem
disturbance. Direct-push technology (DPT), for example,
can be used to install standard 2-inch diameter vacuum
extraction wells, air injection wells, groundwater
depression wells, and monitoring points. Use of DPT
equipment rather than conventional drilling rigs can:
Eliminate drill cuttings and associated waste disposal
Avoid consumption or disposal of drilling fluids, and
Reduce drilling duration by as much as 50-60%.
Evaluating the options for well construction can also
include consideration of potential environmental tradeoffs.
In the case of using DPT, for example, its deployment ease
can reduce fuel-intensive field activities; however,
attempted DPT use at depths approaching the
technology's typical limit (100 feet) could result in wasted
fuel or well installation failure. Another example is the use
of small-diameter injection wells that can lead to large
pressure drops and increase energy consumption of the
system. Additional practices for well construction are
provided in a companion green remediation fact sheet on
remedies using pump and treat technology.3c
Emission of GHG and particulate matter from trucks and
other mobile sources during SVE/AS system construction
can be reduced through use of BMPs such as retrofitting
equipment for cleaner engine exhaust, using ultra low-
sulfur diesel, and reducing idling. More practices are
outlined in Green Remediation Best Management
Practices: Clean Fuel & Emission Technologies for Site
Cleanup
O&M costs at the
former Ferdula landfill
site average below
$500 annually, in
contrast to an estimated
$75,000 per year for
materials, electricity,
and other resources
needed for a
conventional SVE system
meeting the same
remedial goals.
Operating and Monitoring an SVE or AS
SVE and AS system operations can generate high levels of
noise. Adverse impacts on wildlife and local communities
can be reduced prior to system startup through integration
of aboveground equipment housing that contains sound-
proofing material. Acoustic barriers with recycled or
recyclable components may be constructed onsite or
obtained commercially. Use of centrifugal blowers rather
than positive displacement blowers and installation of air-
line mufflers also will decrease noise levels. Other best
practices for preserving vegetation and wildlife habitat
include limiting the removal of trees that obstruct
construction of the extraction or treatment systems and
transplanting any shrubs from proposed extraction points
to other onsite locations.
Additional reductions in land or ecosystem disturbance
and efficiencies can be gained by early consideration of
the site's anticipated reuse. For example, an SVE or AS
pipe network could be constructed in ways allowing for
future integration into the site's utility infrastructure. A
companion fact sheet on excavation and surface
restoration provides more examples of recommended
practices as they relate to each core element of green
remediation.36
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Recommended BMPs for O&M of an SVE or AS system
focus on preserving air quality and reducing energy use,
unnecessary material consumption, and excess waste
generation. Inefficiencies often relate to release of
contaminant vapors through vertical short circuiting,
incomplete treatment of offgases, or migration of vapors
beyond the treatment zone. Unintended vapor emissions
or system inefficiencies can be reduced by:
Adding a low-permeability soil cap at an area with
negative pressure to prevent intrusion of clean air that
can short circuit the extraction system; this option
considers the environmental tradeoffs associated with
cap construction and long-term presence of
impermeable materials such as asphalt or concrete
Ensuring that the zone of influence of vapor extraction
wells completely covers the treatment area
Installing and properly maintaining surface seals around
all wells and monitoring points
Maintaining flow rates sufficient to prevent vapors from
migrating beyond the treatment area without
overloading the treatment system
Using vapor treatment methods appropriate for the
influent vapor concentrations and changing the method
as treatment progresses, and
Regenerating adsorbtive media such as GAC filters.
SVE treatment typically results in an initially high
contaminant loading that decreases over time, prompting
the need for frequent system modifications. Good and
flexible design will reduce needs for modification as site
cleanup advances. Initial deployment of multiple smaller
blowers, for example, can allow some blowers to be shut
down when lower rates of air flow are found to continue
meeting the cleanup objectives. Periodic remedial system
evaluation (RSE) can help identify other system
modifications to increase performance and efficiency,
such as:
Adjusting flow rates to obtain the minimum air flow and
maximum amount of contaminants per volume of vapor
removed
Determining if any well in a manifold system is not
contributing contaminants despite proper well
functioning, and if so, modifying the well or taking it
offline, and
Operating pulsed pumping during off-peak hours of
electrical demand, without compromising cleanup
progress.
Once the bulk of contamination is removed, significant
efficiencies can be gained by switching to a remediation
"polishing" technology with lower energy intensity. One
polishing option is passive SVE, which can be
implemented by installing one-way check valves in well
casings to promote barometric pumping. Environmental
tradeoffs of using passive SVE on a large-scale basis may
involve construction of additional wells.
Decreases in the frequency of field visits and associated
fuel and material consumption or waste generation during
system monitoring can be achieved by:
Increasing automation through use of equipment such
as electronic pressure transducers and thermo-couples
with an automatic data logger (rather than manual
readings) to record data at frequent intervals
Using field test kits or analyzing for only indicator
compounds whenever possible, and
Reducing monitoring frequency and intensity once the
system is optimized.
When a vapor extraction/treatment system is no longer
needed, wells must be properly abandoned and system
elements must be properly decommissioned. System
close-out can include transferring any mobile treatment or
monitoring units to other sites for reuse.
Green Remediation: A Sampling of Success Measures
for SVE or AS Operations
" Reduced electricity consumption through pulsed rather than
continuous air delivery
* Decreased fugitive emission of contaminated vapor due to
properly maintained well seals
* Lower need for potable water as a result of recycling
condenser water for use in supplemental cooling
* Reduced material consumption and waste generation due
to GAC filter regeneration
* Reduced noise disturbance to wildlife and communities
through use of sound-proofed equipment housing
References [Web accessed: 2010, February 28]
1 U.S. EPA; Principles for Greener Cleanups; August 27, 2009;
http://www.epa.gov/oswer/greencleanups
2 U.S. EPA; Green Remediation: Incorporating Sustainable Environmental
Practices into Remediation of Contaminated Sites; EPA 542-R-08-002;
April 2008
3 U.S. EPA; Green Remediation Best Management Practices:
°Bioremediation; EPA 542-F-l 0-006, March 2010
b Site Investigation; EPA 542-F-09-004, December 2009
cPump and Treat Technologies; EPA542-F-09-005, December 2009
JC/eon Fuel & Emission Technologies for Site Cleanup; EPA 542-F-l 0-
008, April 2010
"Excavation and Surface Restoration; EPA542-F-08-012, December
2008
4 U.S. EPA; Off-Gas Treatment Technologies for Soil Vapor Extraction
Systems: State of the Practice; EPA-542-R-05-028, March 2006
5 U.S. EPA OSWER/OSRTI; Green Response and Remedial Action
Contracting and Administrative Toolkit;
http://www.clu in.org/greenremediation/docs/Green_RR_Action_Contra
ct_Admn_Toolkit_July2009.pdf
Visit Green Remediation Focus online:
http://cluin.org/greenremediation
For more information, contact:
Carlos Pachon, OSWER/OSRTI (pachon.carlos@epa.gov)
U.S. Environmental Protection Agency
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