1 dnapl source-zone remediation: how much cleanup & which performance metrics? dnapl source-zone...

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DNAPL Source-Zone Remediation:DNAPL Source-Zone Remediation:How Much Cleanup & Which Performance Metrics?How Much Cleanup & Which Performance Metrics?

DNAPL Source-Zone Remediation:DNAPL Source-Zone Remediation:How Much Cleanup & Which Performance Metrics?How Much Cleanup & Which Performance Metrics?

P. Suresh C. RaoSchool of Civil Engineering

Purdue University

EPA/TIO & ITRC Conference; Chicago, IL

December 10-12, 2002

2

Scope of the Problem

~20,000 sites @$5M/site; cost ~$100 billion

Several source mass depletion technologies have been successfully field tested, but not widely adopted

Need to link DNAPL source treatment with dissolved plume behavior

Need new conceptual framework for site assessment, remediation endpoints & technology integration

3

Questions Considered by the

EPA DNAPL Expert Panel What are the benefits of partial source

depletion? What are the appropriate performance metrics

for assessment of source depletion technologies?

Are available technologies adequate for source characterization to select, (implement), & evaluate mass depletion options?

What performance can be anticipated from available source depletion technologies?

4

Questions Considered by the EPA DNAPL Expert Panel

(contd.) Are currently available tools adequate to

predict the performance of source depletion options?

What are the factors restricting the effective and appropriate adoption of source depletion technologies?

How should decisions be made on whether to undertake source depletion at a site?

What are the potential negative impacts of implementing source depletion technologies?

5

ContaminatedSite

Future Situation

No measures

No NA

Options

Plume Management as an Alternative to DNAPL Source-Zone Treatment

Technical Complexity

Investment CostsO & M Costs

Land Use

moderate

low

high

low

high

high

low

low

low

low

low

high

high

moderate

moderate

moderate

Slide courtesy of Dr. Georg Teutsch, University of Tuebingen

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Options for DNAPL Source Zones

• No Mass Depletion Manage only dissolved plume Contain source & monitor plume

• Partial Mass Depletion Reduce source strength & Monitor plume Enhanced attenuation in plume

• “Complete” Mass Depletion Plume hydraulic control

7

Source & Plume Characterization Issues

2,5

m

TC E m o la r fraction in w ater-6.00 -5.25 -4.50 -3.75 -3.00 -2.25 -1.50 -0.75 -0.01

background saturated

log( )xx

s a t

so

TC E satu ra tion0.00 0.06 0.12 0.18 0.24 0.30 0.36 0.42 >0.48

TCE-Input: 100 Liter / day(2 days)

Increasingpermeability

Gravels, Sandy GravelsSandOpen Framework Gravels

va = 1 m/day

Whittaker et al., 1998

How to assess source & plume strength?

cores in the source?

sample the plume ?

What is the appropriate scale for assessment?

local (point) scale?

integral (plume) scale?

How frequently should we sample?

P1 Pn

OW1 OWn


8

Plume Characterization Issues

True groundwater flow direction

Contaminated site

Source zone(Exact location generally unknown)

Contaminant plumes

Monitoring wells

Assumed groundwater flow direction


9

Benefits of Partial Mass Depletion

Reduction in risks & liabilityDNAPL mobilitysource longevitysource strength

Increased attenuation in plume Reduction in long-term management &

costs Better site stewardship

10

Control Plane & Source Strength

Md = Ji Ai

Ji = Local mass flux (ML2T-1)

qi = Local Darcy flux (LT-1)

Ci = Local conc. (ML-3)

Ai = Area of element i (L2)

Md = Source strength (MT-1)

Ks = Satd. Hyd. Cond (LT-1)

j = Hydraulic gradient (-)

Ji = qi Ci

qi =-Ks j

i

Control Plane (CP)

x

z

Ai = x z

11

Reduced source strength must Modify the dissolved plume behavior Be less than or equal to the

“attenuation capacity” within the

plume Be small enough so that flux-

averaged concentrations at a down-

gradient sentinel well or compliance

control plane are below the regulatory

limits

What are the Criteria for Specifying Source Strength Reduction?

12

Contaminant flux = f (HS, DS)HS - hydrodynamic structureDS – DNAPL architecture

Most contaminated

Least contaminated

Pre-Remediation:

Source Zone

ControlPlane

B

A’

A

B’

ContaminantFlux (Jc)

Source Zone

ControlPlane

B

A’

A

B’

ContaminantFlux (Jc)

Post-Remediation:

Source Management Strategies

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Pre-Remediation:

DissolvedPlume

Control Plane Compliance Plane

Dissolved

Partial Mass Removal:

DNAPL SourceZone


Dissolved

Partial Mass Removal + Enhanced Attenuation:DNAPL SourceZone


DNAPL SourceZone

Plume

Plume

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How does Mass Depletion Change Source Strength?

Source strength should be a strong function of DNAPL source architecture, hydrogeologic heterogeneity & correlation between the two.

To date, there are only a handful of controlled experiments to examine this relationship.

Modeling results provide some guidance.

15

Dover AFB (PCE Release)

0

0.2

0.4

0.6

0.8

1Ethanol In-Situ Flushing Test

0 10.80.60.40.2

Mass Reduction

Sou

rce

Str

engt

h R

educ

tion

Dover AFB: Controlled PCE Release

Brooks et al., 2001

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Modeling Approaches Used

Analytical (heterogeneous v; uniform Sn)

Stream-tube Model (Rao & Jawitz, 2002; Enfield,

2001)

Numerical (heterogeneous v; spatially

correlated Sn)

Lagrangian (Berglund, 1998; Enfield, 2001)

Particle Tracking (Jawitz & Rao, 2002)

Finite Difference T2VOC (Falta & Rao,

2001)

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Coastal Plain Geohydrology used in

T2VOC Simulations

0

5

10

15

z

5

10

15

20

25

10

20

XY

Zperm1.0E-104.6E-112.2E-111.0E-114.6E-122.2E-121.0E-124.6E-132.2E-131.0E-13

Frame 001 22 Oct 2001 Frame 001 22 Oct 2001

Falta & Rao (2001)

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PCE Source Strength: Positive Correlation Between

PCE Content & Permeability

x

z

10 20

5

10

15

20

aqvocflux(kg/m**2*s)3.00E-071.39E-076.46E-083.00E-081.39E-086.46E-093.00E-091.39E-096.46E-103.00E-10


x

z

10 20

5

10

15

20

aqvocflux(kg/m**2*s)3.00E-071.39E-076.46E-083.00E-081.39E-086.46E-093.00E-091.39E-096.46E-103.00E-10


5 yrs 30 yrs

Falta & Rao 2001

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Importance of Correlation:

T2VOC SimulationsCoastal Plain Geology

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Source Removed

Per

cen

t re

du

ctio

n o

f o

ff s

ite

flu

x

Negativecorrelation

Positivecorrelation

Falta & Rao 2001

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Source Strength Reduction by Mass Depletion inUnconsolidated Media

Low efficiency (small ) for homogeneous media (e.g., Borden AFB) Higher efficiency (larger ) for heterogeneous media (Dover AFB) Higher efficiency for negative correlation between permeability & DNAPL content

0 0.2 0.4 0.6 0.8 1.0

0.050.20.5

0.81.52.2

2.5

0

1

Mass depletion (x)str

en

gth

red

ucti

on

(y)

y = x 1/

> 0

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Can Source Strength be Measured?

• Traditional monitoring methods have limitations

• Several new approaches are being developed and field tested (Flux Meter; Tuebingen Pump Tests)

• Only limited field data are available to date

• How reliable are these new methods?

• Are the monitoring costs lower?

• What are the alternatives?

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Estimates of Source Strength

Site Contaminant (Md; g/day)Simpson County, NC MTBE 0.3 to 2.0Vandenberg AFB, CA MTBE 1.2 to 7.0Port Hueneme, CA MTBE 150Elizabeth City, NJ MTBE 4Testfeld Sud, Germany BTEX 1.8

PAHs 29.5Landfill Site, Germany TCE 2.51Alameda Naval Station, CA cis-1,2-DCE 31Nekkar Valley, Germany PCE 77Dover AFB, DE total chlorinated 280St. Joseph, MI total ethenes 425

* adapted from: Einarson & Macaky (2001); ES&T, 35(3):67A-73A

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Current Options for Measuring

Source & Plume Strength Transect of fully screened wells for gw

sampling & hydraulic tests for K and hydraulic head field

Transect of multilevel samplers for gw sampling along with measured K & hydraulic head field

Integrated Pumping Tests; steady & unsteady; single & multiple wells (Tuebingen method)

Transect of Borehole Flux Meters (Florida method)

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Integral-Scale Flow-Rate MeasurementTuebingen Integral Pump Tests

contaminant plume innatural groundwater flow

direction of natural groundwater flow

capture zonesteady state

contaminated site

source zone

contaminant plume at the end of the pumping test

Lt well

(QP, CP)

Qt

Teutsch et al., 2000

Ft= CpQp

Cav = Ft/Qt

Steady state; Single-well

Unsteady; Multi-well


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Comparison at Borden CFB

0.00

1.00

2.00

3.00

4.00

5.00

6.00

Mass

flu

x (g

/d)

ML-discharge +/-34% ML-discharge +/-38%II-discharge +/-40 II-discharge +/-41

Béland-Pelletier et al., 2001

Slide coutesy of Dr Georg Teutsch, Univ of Tuebingen

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Mass Discharge at Two Control Planes:Field Site in Stuttgart, Germany

BTEX mass fluxes at the control planes

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Benzene Toluene Ethylbenzene p-Xylene o-Xylene

Compound

Mas

s Fl

ux [g

/d]

Control Plane I

Control Plane II

PAH mass fluxes at the control planes

0

5

10

15

20

25

30

Nap Any Ace Fln Phe Ant Fth Py

Compound

Mas

s Fl

ux [g

/d]

Control Plane I

Control Plane II

?

0 100 m50

N RiverStreet

Valley Boundary

LiquifiedNatural Gas

Tank

100 m

N

NAPL phase

Pumping WellObservation Well

Control Plane

NAPL in phaseGroundwater flowdirection

Control P

lane I

NT01B73

B72

2069

B42P2

P1

B41

Contaminant Plume

Bockelmann et al., 2001


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Captured Contaminant following a period of exposure

Borehole Flux MeterGroundwater & Contaminant

Fluxes

Dye interceptedin a flux meter

ARC

Hatfield et al., 2001

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Field Installation and Sampling

Courtesy of Mike Annable, Univ of Florida

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0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3

PCE flux (mg/cm2/yr)

Elev

atio

n (c

m) 1st MF

2nd FM3rd FM4th FM

PCE Flux Comparisonat Borden CFB

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30 35

PCE Concentration (mg/L)

Elev

atio

n (c

m)


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0.20.40.60.811.21.41.61.822.22.42.62.83

0.0020.0040.0060.0080.010.0120.0140.0160.0180.020.0220.0240.026

Darcy Velocity (cm /hr)

TCE Flux (m g/cm 2/hr)

creek

GW

AB

C

DE

F

G

H

well

Well Flux 1.12 cm/hr

A B C D E F G H


Borden CFB Test Site

30

30

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Hill AFB Test Site

South North

0 10 20 30 40 50 60 70 80 904650

4660

4670

4680

Distance along cross-section (ft)

Ele

vati

on (

ft) U2-

157

U2-15

5

U2-15

3

U2-15

1

U2-14

9

U2-11

6

U2-14

8

U2-15

0

U2-15

2

U2-15

4

Alpine Clay

Well sorted sand

Silty sand


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Hill AFB Test Site

South North0 10 20 30 40 50 60 70 80 90

4650

4660

4670

4680

Distance along cross-section (ft)

Ele

vati

on (

ft)

U2-15

7

U2-15

5

U2-15

3

U2-15

1

U2-14

9

U2-11

6

U2-14

8

U2-15

0

U2-15

2

U2-15

4

Alpine Clay

Well sorted sand

Silty sand

1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 04 6 6 04 6 6 24 6 6 44 6 6 6

00 . 511 . 522 . 533 . 544 . 555 . 566 . 577 . 588 . 599 . 51 01 0 . 5

0

g/m2/day

Total 180 g/day

20


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Planned U.S. Field Tests for Source Strength Measurements

Dover AFB (test cells) – SERDP Jacksonville Sages Site – SERDP LC-34 site, Cape Canaveral, FL – SERDP Hill AFB, OU2 site, UT – SERDP, ESTCP Port Hueneme, CA – ESTCP, SERDP, AFCEE Waterville Arsenal, NY – ESCTP Fort Lewis, WA – ESTCP Alameda Point, CA – ESTCP

34

Multiple Control-Plane Approach for Measurement of Contaminant Attenuation

tIneControlPlaFluxMass

IIneControlPlaFluxMassRateNA

1*

) (

) ( ln

Slide coutesy of Dr Georg Teutsch, Univ of Tuebingen

35

No Further Degradation Approach??

Distance from Source (x)

Contaminant flux atCompliance Control plane

J(x) = J0 exp [- k v/ x]Source Strength

decay rate constant

GW velocity

Flu

x or

Con

c

ComplianceFlux/Conc

36

Conclusions

The combination of flux-averaged concentrations and source (or plume) strength can be useful for the evaluation of risk and remediation performance.

Robust metrics for site assessment with low resolution (IPT) or high resolution (Flux Meter)

Field-scale comparisons show good agreement with multi-level monitoring fence; other tests underway.

Measurements at multiple control planes and times can provide assessment of evolution of source or plume behavior, and attenuation.

37

Issues in Adopting New Performance Metrics

Further field-scale validation & map a path to regulatory acceptance for source strength approach

Discussion of approaches to source strength reduction (depletion vs barriers vs stabilization)

Large active-use sites vs Smaller, inactive sites Unconsolidated vs fractured media Evaluation of long-term institutional controls Monitoring needs & failure analysis Cost-benefit analysis using appropriate financial

models

1 dnapl source-zone remediation: how much cleanup & which performance metrics? dnapl source-zone...

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