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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