United States Air Force
Air Combat Command
United States
Environmental
Protection
Agency
Office of
Solid Waste and
Emergency Response
Directive No 9355 0-68FS
EPA 540-F-97-004 .^
PB97-963501
April 1997
Presumptive Remedy:
Supplemental Bulletin
Multi-Phase Extraction (MPE)
Technology for VOCs in
Soil and Groundwater
Quick Reference Fact Sheet
This Quick Reference Fact Sheet is issued jointly by the U.S. EPA and Air Combat Command (ACC) of
the United States Air Force (USAF) to provide information on the Multi-Phase Extraction (MPE) technology
for extraction of volatile organic compounds (VOCs) present in soil and groundwater. This fact sheet
recommends MPE as a potentially valuable enhancement for the SVE option under the presumptive
remedy for sites with VOCs in soils.
PURPOSE
BACKGROUND
This Fact Sheet will:
• Provide an explanation of the MPE
technology;
• Explain how to determine if MPE is
applicable to your site;
• Explain how to select between the
three MPE applications;
• Discuss the advantages and
disadvantages of the MPE
applications;
• Provide contaminant extraction
costs for MPE; and
• Provide references and points-of-
contact (POCs) for more information
on MPE.
Presumptive remedies are preferred
technologies for common categories of sites
based on historical patterns of remedy
selection and U.S. EPA's scientific and
engineering evaluation of performance data
on technology implementation. By
streamlining site investigation and
accelerating the remedy selection process,
presumptive remedies are expected to
ensure the consistent selection of remedial
alternatives and reduce time and costs
required to clean up similar sites.
Presumptive remedies are generally
expected to be used at ail appropriate sites;
however, site-specific circumstances dictate
whether a presumptive remedy is
appropriate at a given site. The U.S. EPA
has established presumptive remedies for
sites with soils contaminated by VOCs. The
U.S. EPA guidance documents on these
presumptive remedies are Presumptive
Remedies: Site Characterization and
Technology Selection for CERCLA Sites with
Volatile Organic Compounds in Soils,
OSWER 9355.0-48FS and User's Guide to
the VOCs in Soils Presumptive Remedy.
-35^0
Floor
-------
This fact sheet is a supplemental bulletin for
the VOC Presumptive Remedy. It is intended
to provide site managers with recent
information that may be useful in making
decisions about the specific type of
extraction technology to employ at a VOC,
presumptive remedy site.
What is MPE Technology?
The MPE process was developed for the
remediation of VOCs and other contami-
nants in low to moderate permeability
subsurface formations. The process is a
modification of the conventional soil vapor
extraction (SVE) technology. Traditional SVE
is the process of stripping and extracting
volatile compounds from the soil by inducing
air flow through the soil. Soil vapor flow is
induced by applying a vacuum to extraction
wells. Generally, SVE is applied to soil
above the groundwater table.
MPE is an enhancement of the traditional
SVE system. Unlike SVE, MPE simultane-
ously extracts both groundwater and soil
vapor. The groundwater table is lowered in
order to dewater the saturated zone so that
the SVE process can be applied to the newly
exposed soil. This allows the volatile com-
pounds sorbed on the previously saturated
soil to be stripped by the induced vapor flow
and extracted. In addition, soluble VOCs
present in the extracted groundwater are
also removed.
MPE is a generic term for technologies that
extract soil vapor and groundwater, simul-
taneously. Under this generic term, this fact
sheet presents two technologies, the two-
phase extraction technology (TPE) and the
dual-phase extraction technology (DPE).
Both technologies extract groundwater and
soil vapor from a single well. You can
consider MPE as a tool for VOC remediation
as illustrated in Highlight 1.
The TPE technology employs a high vacuum
(approximately 18 to 26 inches of mercury)
pump to extract both groundwater and soil
vapor from an extraction well. A suction pipe
is lowered into the extraction well to extract
the soil vapor and groundwater from the
subsurface. A typical two-phase type system
is illustrated in Figure 1.
For some TPE methods, turbulence
generated within suction pipe facilitates the
transfer of aqueous phase contaminants to
the vapor phase (up to 98% stripping).
By comparison, the DPE technology
employs a submersible or pneumatic pump
to extract the groundwater, and a high
vacuum (approximately 18 to 26 inches of
mercury) or low vacuum (approximately 3 to
12 inches of mercury) extraction blower is
used to extract the soil vapor as illustrated in
Figure 2. For DPE wells using submersible
pump, a sump is installed at the bottom of
the well to prevent cavitation of the
submersible pump. Under vacuum
conditions, a net positive suction head may
be maintained, to prevent cavitation of the
submersible pump, using a standing water
column. Under high vacuum conditions, a
sump as deep as 20 feet may be required to
provide proper water column at the pump
intake.
Note that some specific hardware and well
configurations associated with the MPE
technologies are patented. In those cases,
potential users should contact the patent
owners about the patent owner's licensing
Highlight 1
Multi-Phase Extraction (MPE) - A remediation
tool for simultaneous extraction of VOC
contaminated soil vapor and groundwater.
The two types of MPE are:
• Two-Phase Extraction (TPE)
• Low or High Vacuum Dual-Phase extraction
(DPE)
-------
requirements. Description, or use of specific
products, methods or companies does not
constitute an endorsement by the USEPA or
the U.S. Air Force's Air Combat Command.
Is MPE Appropriate at my Site?
Once you have determined that your site is a
candidate for a presumptive remedy using
the VOC User's Guide, you must determine
if MPE can be implemented to treat the VOC
contaminated media at your site. MPE is
most cost effective for cleaning up low to
moderate permeability sites with
halogenated VOC contamination in the soil
and groundwater. MPE is also effective at
cleaning up sites contaminated with non-
halogenated VOCs and total petroleum
hydrocarbons (TPH). MPE may be
particularly useful when expedited cleanups
are necessary.
When considering use of MPE, it is
important to choose an engineering firm that
has experience implementing the MPE
technologies. Prior to implementation, a
treatability pilot study should be performed
and the results evaluated to maximize the
effectiveness of the MPE technology
selected.
To determine if the MPE technologies may
be effective at your site, compare your site
conditions to the guidelines presented in
Table 1. These guidelines provide a
preliminary assessment of the basic site
characteristics that relate to MPE treatment
effectiveness. The MPE technologies are
generally applied below the water table.
They also may be applied above and below
the water table simultaneously. Note that if
you wish to apply MPE above the water
table, your site should also meet the air
permeability guidelines. If your site
conditions meet these guidelines, then your
site is a candidate for MPE. At this point you
may wish to select one of the MPE
technologies as the preferred technology for
VOC remedial action at your site and
proceed with a treatability pilot study. These
guidelines are not a definitive screening test
for MPE. So, even if one of your site
conditions does not meet these guidelines,
MPE may still be an appropriate technology
for your site, but greater technical analysis
may be warranted. An engineering
evaluation, by experienced professionals,
should guide your decision to proceed with
an appropriate MPE treatability Pilot Study to
confirm the applicability of the MPE
technologies.
Table 1 . MPE General Guidelines
Site Conditions
Contaminant
Contamination location
Henry's Law Constant of majority of
contaminants
Vapor pressure of majority of contaminants
Geology below groundwater table
Guideline
1 . Halogenated VOCs.
2. Non-Halogenated VOCs and/or Total
Petroleum Hydrocarbons (TPH).
1 . Below groundwater table.
2. Both above and below groundwater table.
> 0.01 at 20 Cs (dimensionless)3
> 1 .0 mm Hg at 20 C9
Sands to Clays
MPE application above the groundwater table
Air permeability of soil above the groundwater
table.
Moderate and low permeability (k< 0.1 darcy0)
soils.
Dimensionless Henry's Law Constant in the form: (concentration in gas phase) / (concentration in liquid phase)
Soil Gas permeability (k): 1 darcy = 1 x 10"8cm2
-------
The effectiveness of the MPE technologies
are directly dependent on site characteristics
including geologic, hydrogeologic, and
contaminant characteristics. The MPE
technologies tend to be less effective under
conditions outside of the guidelines shown
above. MPE has shown to be less effective
for sites that have very high permeabilities
and lithologies consisting primarily of gravels
or cobbles. For effective MPE, the aquifer
must be able to be dewatered. Sites with
extremely high groundwater flow rates may
be not as suitable for MPE. MPE is not
recommended for sites where the target
contaminants are not volatile compounds
(i.e. inorganic and semi-volatile).
Which Type of MPE is Best for my Site?
Once you have determined that a MPE
technology will be effective at your site, you
must determine which variation of MPE will
be most effective for contaminant removal.
All of the MPE technologies; low-vacuum
DPE (LVDPE), high-vacuum DPE (HVDPE),
or TPE, have optimum site conditions where
they are considered to be the most cost
effective for VOC contaminant removal. To
determine which MPE technology will be
most effective at your site, compare your site
conditions to the guidelines presented in
Table 2. These guidelines provide a
preliminary assessment of the basic site
characteristics that relate to potential
treatment effectiveness of LVDPE, HVDPE,
and TPE.
Table 2. MPE Technology Selection Guide: LVDPE, HVDPE, or TPE
Site
Conditions
Groundwater production
rate3
Maximum depth of
targeted contamination
Geology below
groundwater table
LVDPE
Guideline
not limited by
typical groundwater
production rate,
however aquifer
must be able to be
dewatered.
not limited by depth
of contaminant
Sands to silty sands
HVDPE
Guideline
not limited by
typical
groundwater
production rate,
however aquifer
must be able to
be dewatered.
Not limited by
depth of
contaminant
Sandy silts to
clays
TPE
Guideline
<5 gpm
1 . Up to 50V feet below
ground surface bgs
(for groundwater
production < 2 gpm).
2. Up to 20-30 feet bgs
(for groundwater
production
between 2 and 5
gpm).
Sandy silts to clays
For MPE application above the groundwater table
Air permeability of soil
above the groundwater
table.
Moderate
permeability
(greater than 1 x
10"3darcy)
Low
permeability
(less than 1 x
10~2darcy)
Low permeability (less
than 1 x10"2darcy)
For MPE, the aquifer must be able to be dewatered.
-------
Generally, the high vacuum (approximately
18-26 inches mercury) applications, HVDPE
and TPE, are most cost effective where the
target geologic formations have low
permeabilities (i.e., sandy silts to clays). Both
HVDPE and TPE will be effective at depths
less than 50 feet BGS with low ground water
production rates (<5 gpm). However,
HVDPE has a broader range of application
and may also be applied at greater depths
and higher flow rates.
The low vacuum (3 to 12 inches of mercury)
application, LVDPE, is suitable for more
permeable soils (i.e., sands to silty sands).
LVDPE is not limited by depth of
commitment or typical groundwater flow
rates, however the aquifer must be able to
be dewatered. Generally MPE is applied
below the groundwater table. However, MPE
may also be applied simultaneously above
and below the water table. Where MPE is to
be applied above the groundwater table, the
air permeability must also be considered.
Figure 3 presents a decision logic flowchart
that may assist you in the selection of
LVDPE, HVDPE, or TPE.
Prior to implementation of the chosen MPE
technology, a treatability pilot study should
be performed by an experienced engineering
firm. Proper interpretation of the pilot study
results are needed to maximize the
effectiveness of MPE.
Case Studies and Costs
The MPE technology has been applied at
dozens of low to moderate permeability sites
and has consistently proven to be more
effective at removing subsurface VOCs than
conventional pump-and-treat or soil vapor
extraction systems alone. This is due to the
increase in groundwater and contaminated
soil vapor removal rates, and the
volatilization of contaminants in the
previously saturated soils. The increased
mass removal rates result in decreased total
removal costs. Note that the effectiveness of
the MPE technologies are directly dependent
on site characteristics (geologic,
hyrogeologic, and contaminant
characteristics, etc).
Pilot study and/or full-scale MPE system
field data, demonstrating the
effectiveness of MPE at multiple military
sites (including McClellan AFB, Travis AFB,
Nellis AFB, FE Warren AFB, Offutt AFB,
Ellsworth AFB, DDRW-Tracy Depot, and Air
Force Plant-44 [AFP-44]) are currently
available. Appendix A presents the results of
selected case studies. Appendix A also
includes estimated full-scale contaminant
extraction costs, presented in dollars per
pound of contaminant removed ($/lb), for
each of the case studies. These costs are
based on a single well extraction system
operated for one year. They include capital
costs, installation costs and operation and
maintenance costs. The costs do not include
design, well installation, or soil
vapor/groundwater treatment costs. These
costs also do not include any costs
associated with patent requirements. As
demonstrated in Appendix A, the
contaminant extraction costs for MPE
applications are highly site-specific. It is
dependent upon the original and target
clean-up level concentrations of
contaminants, aquifer/vadose zone
characteristics, groundwater and vapor
flowrates, as well as the design and
operation of the technology used.
-------
LESSONS LEARNED
The key to designing an effective MPE
system is experience and performing a
treatability pilot study beforehand. Pilot study
results provide key parameters, such as
effective well vacuum, groundwater and
vapor radii of influence, and groundwater
and soil vapor extraction flowrates. These
parameters are essential for the selection
and design of vacuum pumps, submersible
pumps, and eventually, groundwater and
vapor treatment.
Because TPE and HVDPE application
parameters overlap, other site parameters
will also affect your decision on which MPE
technology to use. The ability to use existing
extraction wells at a site may be the key
factor in deciding to use HVDPE or TPE.
Table 3 provides the advantages and
disadvantages of HVDPE, LVDPE, TPE
which may assist you in final selection of a
MPE technology.
Table 3. Advantages and Disadvantages Between HVDPE/LVDPE and TPE
HVDPE and LVDPE
TPE
Advantages
No limitation on depth of targeted
contamination.
Lower vacuum losses within extraction
well.
No limitation on groundwater production
rate.
Groundwater stripping: up to 98%
transfer of aqueous phase
contaminants to vapor phase.
No pumps or mechanical equipment
required in well.
Can be applied at existing extraction
or monitoring wells.
Disadvantages
Where submersible pumps are used, a
standing water column above the pump
is required, therefore, installation of a
new extraction well with a sump may be
required.
More controls required for pump as
compared with TPE.
Limited to a maximum groundwater
depth of approximately 50 feet below
ground surface.
Limited to a maximum groundwater
flowrate of approximately 5 gpm.
Higher vacuum losses due to lifting
water from the well.
-------
CONCLUSION
For sites with VOC-contamination in the soil
and/or groundwater and appropriate site
characteristics, MPE is a cost effective
technology. MPE has been applied at
dozens of low- to moderate-permeability
sites and has consistently proven to be more
effective at removing subsurface VOCs than
conventional pump-and-treat or soil-vapor
extraction systems alone. For further
information or assistance on MPE
applications, refer to Table 4 for points of
contact or reference information.
Table 4. MPE Points-of-Contact and References
Points of
Contact
Affiliation
Name
Title
Phone
Number
Site Contacts DDRW-Tracy Marshall Cloud Project Manager/ (209)982-2086
Environmental
Specialist
Travis AFB Mark Sandy Remedial Program (707)424-3172
Manager
NeiiisAFB JirnPedrick Chief of Environmental (702) 652-6 i 03
Restoration Division
McCieilanAFB Kevin Wong Remedial Program (9 i 6) 643-0830
Manager
~FE Warren"AFB Barry Mountain Chief of Missiie (307)-775-2532
Engineering
Ellsworth AFB John DeYoe Remedial Program (665)385-2675
Manager
OffuttAFB Phil Cork Installation Restoration (402) 294-762i
Program Manager
Wright-Patterson AFB Dennis Scott Remedial Program (513)255-0258
(AFP-44) Manager x417
EPA Contacts U.S.EPA Headquarters Scott Fredericks Environmental (703)603-8771
Protection Specialist
IIIirU-S'lPAH^gi^^ ~~~ (Z0?)603^836
~'u'.'s"EPA Headquarters Jo'h"n'B'ian"cn'ard P.E. (103)603-9031"
ACC Contacts ACC Headquarters Margaret Program Manager (757) 764-6249
Patterson
Existing U.S.EPA Guidance "Presumptive Remedies: Site Characterization and Technology
Selection for CERCLA Sites with Volatile Organic Compounds in
Soils,".OSWER 9355JM8FS.
"Presumptive Response Strategy and Ex-Situ Treatment Technologies
for Contaminated Groundwater at CERCLA Sites," Final, October
1996, OSWER 9283.1-12.
"User's Guide to the VOCs in Soils Presumptive Remedy," April 1996.
-------
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Are
Halogenated
VOCs Present in the
Groundwater
9
Are
Non-Haiogenated
VOCs or TPH Present in
the Groundwater
9
MPE Is Not
Applicable
at This Site
Is
A Timely
Cleanup
Necessary
Other Technologies
May Be More Applicable
Is the
Saturated Zone
Composed of Sands
to Silty Sands
Is the
Saturated Zone
Composed of Sandy
Silts to Clays
Is the
Depth to
Groundwater
<50 Feet bgs
Can
Extraction
Well with Sump be
Installed
9
Are
Pneumatic Pumps
Applicable
Other Technologies
May Be More Applicable
Can
Extraction
Well with Sump be
Installed
Can
Aquifer be
Dewatered with
LVDPE
9
Are
Pneumatic
Pumps
Applicable
Data Suggests LVDPE
Should Be Applied
Is the
Permeability
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Moderate (>1 x10J
Darcy)
?
is the
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Contaminated
Data Suggests LVDPE
will be Most
Effective Applied to
Both the Saturated Zone
and the Vadose Zone
Data Suggests LVDPE
will be Most
Effective Applied
to the Saturated
Zone Only
-------
Can
Aquifer be
Dewatered
with TPE
9
Is the
Groundwater
Flowrate
<5 gpm
X
Data Suggests TPE
Should Be Applied
TPE Applicability
Can
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9
Vadose Zone
Contaminated
with VOCs
Data Suggests HVDPE
Data Suggests HVDPE
will be Most
Effective Applied to
will be Most
Effective Applied
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Zone Only
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Figure 3.
MPE Selection Decision
Logic Diagram
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