Multiphase Extraction for Soil and Groundwater Remediation Nick Swiger Spring 2007

Multiphase Multiphase Extraction for Soil Extraction for Soil and Groundwater and Groundwater

RemediationRemediationNick SwigerNick Swiger

Spring 2007Spring 2007

IntroductionIntroduction

Contaminant ReleasesContaminant Releases When a contaminant is released into the When a contaminant is released into the

environment, it will partition into four phases.environment, it will partition into four phases. Bulk liquid if insoluble (LNAPL or DNAPL) Bulk liquid if insoluble (LNAPL or DNAPL) Adsorb to soil particlesAdsorb to soil particles Vapor phase in soil gasVapor phase in soil gas Dissolve into soil moistureDissolve into soil moisture

To effectively remediate the environment from a To effectively remediate the environment from a chemical spill, all phases will need to be chemical spill, all phases will need to be recovered.recovered.

Types of remediation systems have greatly Types of remediation systems have greatly evolved in last 20 years as everyone is always evolved in last 20 years as everyone is always looking for a more effective and efficient process.looking for a more effective and efficient process.

Multiphase extraction is a relatively “new” Multiphase extraction is a relatively “new” enhancement to soil vapor extraction.enhancement to soil vapor extraction.

What is Multiphase What is Multiphase Extraction?Extraction?

Extractions of multiple phases of fluids from the Extractions of multiple phases of fluids from the subsurface.subsurface.

Fairly recent enhancement for the increased Fairly recent enhancement for the increased recovery and efficiency (in right subsurface recovery and efficiency (in right subsurface conditions) of Soil Vapor Extractions.conditions) of Soil Vapor Extractions.

Two Types:Two Types: Dual Phase Extraction (Not focused on in Dual Phase Extraction (Not focused on in

paper/presentation)paper/presentation) Extraction of multiple phases of fluids utilizing separate pumps Extraction of multiple phases of fluids utilizing separate pumps

and conduits. For example, installing a submersible pump in a and conduits. For example, installing a submersible pump in a well to lower the elevation of the groundwater to enhance an well to lower the elevation of the groundwater to enhance an existing soil vapor extraction system.existing soil vapor extraction system.

Multiphase ExtractionMultiphase Extraction Extraction of multiple phases of fluids utilizing one pump and Extraction of multiple phases of fluids utilizing one pump and

one conduit.one conduit.

Typical Schematic of Typical Schematic of Multiphase ExtractionMultiphase Extraction

Multiphase Extraction vs. Multiphase Extraction vs. Soil Vapor ExtractionSoil Vapor Extraction

Both vapor and hydraulic conductivity are a Both vapor and hydraulic conductivity are a function of moisture content in the vadose zone.function of moisture content in the vadose zone. Vapor conductivity decreases with increasing moisture Vapor conductivity decreases with increasing moisture

content.content. With many chemical releases, they will migrate With many chemical releases, they will migrate

vertically until a lower permeability unit is vertically until a lower permeability unit is reached or the surface of the saturated soil is reached or the surface of the saturated soil is reached (capillary fringe above the reached (capillary fringe above the groundwater).groundwater). Chemicals with a lower density than water (LNAPL) Chemicals with a lower density than water (LNAPL)

with stop at the saturated soil.with stop at the saturated soil. Chemicals with a higher density than water (DNAPL) Chemicals with a higher density than water (DNAPL)

with stop at a lower permeability unit or force balance with stop at a lower permeability unit or force balance (i.e. capillary, hydrostatic, etc.)(i.e. capillary, hydrostatic, etc.)

Multiphase Extraction vs. Multiphase Extraction vs. Soil Vapor Extraction cont.Soil Vapor Extraction cont.

In both cases, the areas typically In both cases, the areas typically with the majority of the contaminants with the majority of the contaminants have a high moisture content.have a high moisture content. The decreased vapor conductivity in the The decreased vapor conductivity in the

areas with the majority of the areas with the majority of the contaminants makes soil vapor contaminants makes soil vapor extraction less efficient.extraction less efficient.

The increased moisture content also The increased moisture content also limits the mass transfer of contaminants limits the mass transfer of contaminants from the liquid phase to vapor phase.from the liquid phase to vapor phase.


The mass transfer limited systems The mass transfer limited systems are less efficient than flow limited are less efficient than flow limited systems.systems. Mass transfer in high moisture content Mass transfer in high moisture content

dominated by Henry’s Lawdominated by Henry’s Law KKHH = Cv/Cl (conc. vapor/conc. liquid) = Cv/Cl (conc. vapor/conc. liquid) Exponential Decrease vs. Linear DecreaseExponential Decrease vs. Linear Decrease


By the removal of multiple phases of fluids By the removal of multiple phases of fluids it forces systems to be flow limited.it forces systems to be flow limited.

Time

Mon

thly

Mass

Rem

ove

d

Typical Uses of Multiphase Typical Uses of Multiphase ExtractionExtraction

As with soil vapor extraction, the volatile compounds that tend As with soil vapor extraction, the volatile compounds that tend not to adhere to the soil are amenable to multiphase extraction. not to adhere to the soil are amenable to multiphase extraction. The following chemical properties are typically used for The following chemical properties are typically used for indicators.indicators. Relatively low distribution coefficient (ratio of concentration in soil Relatively low distribution coefficient (ratio of concentration in soil

to concentration in liquid)to concentration in liquid) Kd = Cs/ClKd = Cs/Cl

Relatively high vapor pressure (pressure exerted by vapor in Relatively high vapor pressure (pressure exerted by vapor in equilibrium with bulk fluid)equilibrium with bulk fluid)

Indicative of the compounds volatility or tendency to exist in gaseous Indicative of the compounds volatility or tendency to exist in gaseous phase.phase.

Multiphase extraction is most efficient in porous media with Multiphase extraction is most efficient in porous media with moderate permeability – allows removal of both phases with the moderate permeability – allows removal of both phases with the greatest remedial influence.greatest remedial influence. Highly permeable media, the dominant phase removed will be water Highly permeable media, the dominant phase removed will be water

and there will be less influence on the soil gas. Near the aquifer, and there will be less influence on the soil gas. Near the aquifer, mostly groundwater removed with very little soil gas.mostly groundwater removed with very little soil gas.

Low permeable media, the dominant phase removed will be gas, but Low permeable media, the dominant phase removed will be gas, but the water will have much less influence. Near aquifer, there will be the water will have much less influence. Near aquifer, there will be much drawdown, with little influence on the vadose zone.much drawdown, with little influence on the vadose zone.

Contaminant Removal with Contaminant Removal with Multiphase ExtractionMultiphase Extraction

Phase removal can be accomplished Phase removal can be accomplished by two mechanisms:by two mechanisms: Overcoming hydrostatic pressure (static Overcoming hydrostatic pressure (static

lift)lift) Entraining the liquids in the vaporEntraining the liquids in the vapor

Dependant on vapor velocityDependant on vapor velocity


For the static lift/hydrostatic For the static lift/hydrostatic pressure, the vacuum applied must pressure, the vacuum applied must be able to lift the most dense phase be able to lift the most dense phase fluid (water with an LNAPL spill and fluid (water with an LNAPL spill and contaminant with a DNAPL spill) to contaminant with a DNAPL spill) to the surface and overcome major and the surface and overcome major and minor losses.minor losses. P = P = ρρgh (h – height of lift + head loss)gh (h – height of lift + head loss)


For the liquid to be removed via vapor For the liquid to be removed via vapor entrainment, the vapor velocity forces entrainment, the vapor velocity forces [drag (F[drag (Fdd) and vapor surface forces ) and vapor surface forces (F(Fvv)] must overcome gravity forces (F)] must overcome gravity forces (Fgg):): FFgg < F < Fdd + F + Fvv

FFg g = = ρρww*V*g = mg *V*g = mg

FFdd = 0.5*Cd* = 0.5*Cd* ρρaa*v*v22*A*A

FFvv = = ρρaa*A*v*A*v22


Three different schemes of multiphase Three different schemes of multiphase flow in well (based on velocity of the flow in well (based on velocity of the vapor)vapor)

Multiphase Extraction Multiphase Extraction OperationsOperations

Two extraction configurations are Two extraction configurations are typically utilized and are based on typically utilized and are based on the location of the applied vacuum.the location of the applied vacuum. Vacuum can be applied down in the well Vacuum can be applied down in the well

with the use of a “stinger” or “drop” with the use of a “stinger” or “drop” tube.tube.

Vacuum can be applied to the top of the Vacuum can be applied to the top of the well.well.


The “stinger” tube configuration The “stinger” tube configuration would be most applicable very near would be most applicable very near or at the water table.or at the water table.

The vacuum configuration would be The vacuum configuration would be more applicable the high moisture more applicable the high moisture content soil in the vadose zonecontent soil in the vadose zone


The fluid removal is provided by a fan, The fluid removal is provided by a fan, compressor blower, or pump depending on compressor blower, or pump depending on the subsurface conditions (i.e. flow rate the subsurface conditions (i.e. flow rate needed, vacuum needed, etc.).needed, vacuum needed, etc.).

With all fans, blowers, and compressors With all fans, blowers, and compressors the fluid stream must be routed through a the fluid stream must be routed through a tank, commonly called a knockout tank, as tank, commonly called a knockout tank, as they are not designed for liquid movement.they are not designed for liquid movement. Liquid ring pumps do not need to have a Liquid ring pumps do not need to have a

knockout tank – designed for multiple phase knockout tank – designed for multiple phase fluids.fluids.


All phases of fluids will have to be treated All phases of fluids will have to be treated prior to discharge (for the most part – prior to discharge (for the most part – depending on regulations); however, with depending on regulations); however, with non aqueous phase contaminants, there non aqueous phase contaminants, there will be minimal treatment of water as the will be minimal treatment of water as the vapor acts as in situ air stripping.vapor acts as in situ air stripping. Multiple ways to treat the fluids such as Multiple ways to treat the fluids such as

chemical (i.e. oxidation with ozone or chemical (i.e. oxidation with ozone or peroxide), physical (i.e. carbon adsorption), peroxide), physical (i.e. carbon adsorption), and biological (i.e. bioreactors)and biological (i.e. bioreactors)

Determining Treatment Determining Treatment AreaArea

Each extraction point will have a set “area Each extraction point will have a set “area of influence” or “radius of influence” if of influence” or “radius of influence” if radial flow is assumed.radial flow is assumed. Darcy’s Law can be used in both the saturated Darcy’s Law can be used in both the saturated

and unsaturated media to approximate radius of and unsaturated media to approximate radius of influence (capture).influence (capture).

Integrated, steady state Darcy’s Law for unconfined Integrated, steady state Darcy’s Law for unconfined aquifers:aquifers:

Q = [K2π (HoQ = [K2π (Ho22-Hw-Hw22)] / ln (Ri/Rw) )] / ln (Ri/Rw) Where:Where: Ho – original water elevationHo – original water elevation Hw – water elevation in extraction wellHw – water elevation in extraction well Ri – radius of influenceRi – radius of influence Rw – radius of extraction wellRw – radius of extraction well


For the vadose zone, the Darcy’s Flux, related to pressure changes For the vadose zone, the Darcy’s Flux, related to pressure changes (instead of head) is:(instead of head) is:

q = -k/µ (dP/dx) q = -k/µ (dP/dx) Using the above and flow equations for radial flow to wells, Jeff Kuo in Using the above and flow equations for radial flow to wells, Jeff Kuo in

Practical Design Calculations for Soil and Groundwater Remediation Practical Design Calculations for Soil and Groundwater Remediation presented the following:presented the following:

uuww = (k/2µ){P = (k/2µ){Pww/[ R/[ Rww (ln (R (ln (Rww/R/Rii)]}[1-(P)]}[1-(Priri/P/Pww))22]]

where: uwhere: uww - vapor flux at the extraction well - vapor flux at the extraction well PPww - pressure at the extraction well - pressure at the extraction well PPriri - pressure at the radius of influence - pressure at the radius of influence RRw w - radius of the extraction well- radius of the extraction well RRii - radius of influence - radius of influence

uurr = (k/2µ) = (k/2µ){{{P{Pww/[ r (ln (R/[ r (ln (Rww/R/Rii)]}[1-(P)]}[1-(Priri/P/Pww)2]/ {1 + [1-(P)2]/ {1 + [1-(Priri/P/Pww))22] [(ln ] [(ln (r/R(r/Rww)/ln (R)/ln (Rww/R/Rriri)]})]}0.50.5}}

where:where: uurr - vapor velocity at r - vapor velocity at r r – radial distance rr – radial distance r


The two equations can be utilized to The two equations can be utilized to find the capture area in the vadose find the capture area in the vadose zone and vapor velocity at certain zone and vapor velocity at certain radial points with in the vadose radial points with in the vadose zone.zone. May soil and groundwater remediation May soil and groundwater remediation

engineers utilize only the “radius of engineers utilize only the “radius of influence” as the soil gas capture.influence” as the soil gas capture. This provides the extent of capture, but not This provides the extent of capture, but not

necessarily the extent of remediation!!!!!necessarily the extent of remediation!!!!!

SummarySummary Multiphase extraction is a enhancement that can be made Multiphase extraction is a enhancement that can be made

to soil vapor extraction system to increase efficiency of to soil vapor extraction system to increase efficiency of remediation of volatile, moderately soluble, low soil remediation of volatile, moderately soluble, low soil adsorption, chemicals in the vadose zones with higher adsorption, chemicals in the vadose zones with higher moisture contents.moisture contents.

The most efficient use of multiphase extraction is with The most efficient use of multiphase extraction is with moderately permeable porous media, so both phases of moderately permeable porous media, so both phases of fluids can be extracted.fluids can be extracted.

Can apply vacuum to the top of well (mostly in high Can apply vacuum to the top of well (mostly in high moisture content vadose zone) or with a “stinger” pipe moisture content vadose zone) or with a “stinger” pipe (mostly near the surface of the aquifer/capillary fringe).(mostly near the surface of the aquifer/capillary fringe).

The extraction can be accomplished with many types of fluid The extraction can be accomplished with many types of fluid pumps, but must have a knockout tank with all except a pumps, but must have a knockout tank with all except a liquid ring pump. The fluids will have to treated prior to liquid ring pump. The fluids will have to treated prior to discharge.discharge.

The extent of remediation can be determined by Darcy’s The extent of remediation can be determined by Darcy’s Law. In the vadose zone, caution must be used as the zone Law. In the vadose zone, caution must be used as the zone of vapor capture is not necessarily the zone of remediation.of vapor capture is not necessarily the zone of remediation.

Questions or Questions or Comments?Comments?

[email protected]@uidaho.edu or or

[email protected]@michigan.gov

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Multiphase Extraction for Soil and Groundwater Remediation Nick Swiger Spring 2007