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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
6
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
Slide courtesy of Dr. Georg Teutsch, University of Tuebingen
8
Plume Characterization Issues
True groundwater flow direction
Contaminated site
Source zone(Exact location generally unknown)
Contaminant plumes
Monitoring wells
Assumed groundwater flow direction
Slide courtesy of Dr. Georg Teutsch, University of Tuebingen
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
13
Pre-Remediation:
DissolvedPlume
Control Plane Compliance Plane
Dissolved
Partial Mass Removal:
DNAPL SourceZone
Control Plane Compliance Plane
Dissolved
Partial Mass Removal + Enhanced Attenuation:DNAPL SourceZone
Control Plane Compliance Plane
DNAPL SourceZone
Plume
Plume
14
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
16
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)
17
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)
18
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
Frame 001 22 Oct 2001 Frame 001 22 Oct 2001
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
Frame 001 22 Oct 2001 Frame 001 22 Oct 2001
5 yrs 30 yrs
Falta & Rao 2001
19
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
20
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
21
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?
22
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
23
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)
24
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
Slide courtesy of Dr. Georg Teutsch, University of Tuebingen
25
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
26
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
Slide courtesy of Dr. Georg Teutsch, University of Tuebingen
27
Captured Contaminant following a period of exposure
Borehole Flux MeterGroundwater & Contaminant
Fluxes
Dye interceptedin a flux meter
ARC
Hatfield et al., 2001
28
Field Installation and Sampling
Courtesy of Mike Annable, Univ of Florida
29
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)
Courtesy of Mike Annable, Univ of Florida
30
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
Courtesy of Mike Annable, Univ of Florida
Borden CFB Test Site
30
30
31
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
Courtesy of Mike Annable, Univ of Florida
32
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
Courtesy of Mike Annable, Univ of Florida
33
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