Multiphase Extraction for
Soil and Groundwater
Remediation
Nick Swiger
Spring 2007
Introduction
Contaminant Releases

When a contaminant is released into the environment, it will
partition into four phases.
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Bulk liquid if insoluble (LNAPL or DNAPL)
Adsorb to soil particles
Vapor phase in soil gas
Dissolve into soil moisture
To effectively remediate the environment from a chemical spill,
all phases will need to be recovered.
Types of remediation systems have greatly evolved in last 20
years as everyone is always looking for a more effective and
efficient process.
Multiphase extraction is a relatively “new” enhancement to soil
vapor extraction.
What is Multiphase Extraction?
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Extractions of multiple phases of fluids from the subsurface.
Fairly recent enhancement for the increased recovery and
efficiency (in right subsurface conditions) of Soil Vapor
Extractions.
Two Types:
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Dual Phase Extraction (Not focused on in paper/presentation)
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Extraction of multiple phases of fluids utilizing separate pumps and
conduits. For example, installing a submersible pump in a well to lower the
elevation of the groundwater to enhance an existing soil vapor extraction
system.
Multiphase Extraction
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Extraction of multiple phases of fluids utilizing one pump and one conduit.
Typical Schematic of Multiphase
Extraction
Multiphase Extraction vs. Soil Vapor
Extraction
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Both vapor and hydraulic conductivity are a function of
moisture content in the vadose zone.
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Vapor conductivity decreases with increasing moisture content.
With many chemical releases, they will migrate vertically until a
lower permeability unit is reached or the surface of the saturated
soil is reached (capillary fringe above the groundwater).
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Chemicals with a lower density than water (LNAPL) with stop at the
saturated soil.
Chemicals with a higher density than water (DNAPL) with stop at a lower
permeability unit or force balance (i.e. capillary, hydrostatic, etc.)
Multiphase Extraction vs. Soil Vapor
Extraction cont.
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In both cases, the areas typically with the
majority of the contaminants have a high
moisture content.
The decreased vapor conductivity in the areas with
the majority of the contaminants makes soil vapor
extraction less efficient.
 The increased moisture content also limits the mass
transfer of contaminants from the liquid phase to
vapor phase.
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Multiphase Extraction vs. Soil Vapor
Extraction cont.
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The mass transfer limited systems are less
efficient than flow limited systems.
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Mass transfer in high moisture content dominated by
Henry’s Law
KH = Cv/Cl (conc. vapor/conc. liquid)
 Exponential Decrease vs. Linear Decrease
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Multiphase Extraction vs. Soil Vapor
Extraction cont.
By the removal of multiple phases of fluids it forces
systems to be flow limited.
Monthly Mass Removed
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Time
Typical Uses of Multiphase
Extraction
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As with soil vapor extraction, the volatile compounds that tend not to adhere
to the soil are amenable to multiphase extraction. The following chemical
properties are typically used for indicators.
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Relatively low distribution coefficient (ratio of concentration in soil to
concentration in liquid)
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Relatively high vapor pressure (pressure exerted by vapor in equilibrium with bulk
fluid)
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Kd = Cs/Cl
Indicative of the compounds volatility or tendency to exist in gaseous phase.
Multiphase extraction is most efficient in porous media with moderate
permeability – allows removal of both phases with the greatest remedial
influence.
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Highly permeable media, the dominant phase removed will be water and there will
be less influence on the soil gas. Near the aquifer, mostly groundwater removed
with very little soil gas.
Low permeable media, the dominant phase removed will be gas, but the water will
have much less influence. Near aquifer, there will be much drawdown, with little
influence on the vadose zone.
Contaminant Removal with
Multiphase Extraction
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Phase removal can be accomplished by two
mechanisms:
Overcoming hydrostatic pressure (static lift)
 Entraining the liquids in the vapor
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Dependant on vapor velocity
Contaminant Removal with
Multiphase Extraction
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For the static lift/hydrostatic pressure, the
vacuum applied must be able to lift the most
dense phase fluid (water with an LNAPL spill
and contaminant with a DNAPL spill) to the
surface and overcome major and minor losses.
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P = ρgh (h – height of lift + head loss)
Contaminant Removal with
Multiphase Extraction
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For the liquid to be removed via vapor
entrainment, the vapor velocity forces [drag (Fd)
and vapor surface forces (Fv)] must overcome
gravity forces (Fg):
Fg < Fd + Fv
 Fg = ρw*V*g = mg
 Fd = 0.5*Cd* ρa*v2*A
 Fv = ρa*A*v2
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Contaminant Removal with
Multiphase Extraction
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Three different schemes of multiphase flow in well
(based on velocity of the vapor)
Multiphase Extraction Operations
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Two extraction configurations are typically
utilized and are based on the location of the
applied vacuum.
Vacuum can be applied down in the well with the
use of a “stinger” or “drop” tube.
 Vacuum can be applied to the top of the well.
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Multiphase Extraction Operations
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The “stinger” tube configuration would be most
applicable very near or at the water table.
The vacuum configuration would be more
applicable the high moisture content soil in the
vadose zone
Multiphase Extraction Operations
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The fluid removal is provided by a fan, compressor
blower, or pump depending on the subsurface
conditions (i.e. flow rate needed, vacuum needed, etc.).
With all fans, blowers, and compressors the fluid stream
must be routed through a tank, commonly called a
knockout tank, as they are not designed for liquid
movement.
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Liquid ring pumps do not need to have a knockout tank –
designed for multiple phase fluids.
Multiphase Extraction Operations
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All phases of fluids will have to be treated prior
to discharge (for the most part – depending on
regulations); however, with non aqueous phase
contaminants, there will be minimal treatment
of water as the vapor acts as in situ air stripping.
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Multiple ways to treat the fluids such as chemical (i.e.
oxidation with ozone or peroxide), physical (i.e.
carbon adsorption), and biological (i.e. bioreactors)
Determining Treatment Area
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Each extraction point will have a set “area of
influence” or “radius of influence” if radial flow is
assumed.
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Darcy’s Law can be used in both the saturated and
unsaturated media to approximate radius of influence
(capture).
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Integrated, steady state Darcy’s Law for unconfined aquifers:
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Q = [K2π (Ho2-Hw2)] / ln (Ri/Rw)
Where:
Ho – original water elevation
Hw – water elevation in extraction well
Ri – radius of influence
Rw – radius of extraction well
Determining Treatment Area
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For the vadose zone, the Darcy’s Flux, related to pressure changes (instead of head) is:
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q = -k/µ (dP/dx)
Using the above and flow equations for radial flow to wells, Jeff Kuo in Practical
Design Calculations for Soil and Groundwater Remediation presented the following:
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uw = (k/2µ){Pw/[ Rw (ln (Rw/Ri)]}[1-(Pri/Pw)2]
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where: uw - vapor flux at the extraction well
Pw - pressure at the extraction well
Pri - pressure at the radius of influence
Rw - radius of the extraction well
Ri - radius of influence
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ur = (k/2µ){{Pw/[ r (ln (Rw/Ri)]}[1-(Pri/Pw)2]/ {1 + [1-(Pri/Pw)2] [(ln (r/Rw)/ln
(Rw/Rri)]}0.5}
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where:
ur - vapor velocity at r
r – radial distance r
Determining Treatment Area
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The two equations can be utilized to find the
capture area in the vadose zone and vapor
velocity at certain radial points with in the
vadose zone.
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May soil and groundwater remediation engineers
utilize only the “radius of influence” as the soil gas
capture.
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This provides the extent of capture, but not necessarily
the extent of remediation!!!!!
Summary
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Multiphase extraction is a enhancement that can be made to soil vapor
extraction system to increase efficiency of remediation of volatile, moderately
soluble, low soil adsorption, chemicals in the vadose zones with higher
moisture contents.
The most efficient use of multiphase extraction is with moderately permeable
porous media, so both phases of fluids can be extracted.
Can apply vacuum to the top of well (mostly in high moisture content vadose
zone) or with a “stinger” pipe (mostly near the surface of the
aquifer/capillary fringe).
The extraction can be accomplished with many types of fluid pumps, but
must have a knockout tank with all except a liquid ring pump. The fluids will
have to treated prior to discharge.
The extent of remediation can be determined by Darcy’s Law. In the vadose
zone, caution must be used as the zone of vapor capture is not necessarily the
zone of remediation.
Questions or
Comments?
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