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1 Office of Research and DevelopmentNational Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, Ada, Oklahoma
Flux-Based DNAPL SiteRemediation: Field Case StudiesSuresh Rao, School of Civil Engineering, Purdue University
Triad Conference – June 10, 2008
0 10 20 30 40 50 60 70 80 90
4660
4665
0 10 20 30 40 50 60 70 80 90
4660
4665
4670
0 10 20 30 40 50 60 70 80 90
4660
4665
0 10 20 30 40 50 60 70 80 90
4660
4665
4670
0 10 20 30 40 50 60 70 80 90
4660
4665
0 10 20 30 40 50 60 70 80 90
4660
4665
4670
Control Plane
z
y
x
nJ
q0
2
Flux-Based Characterizationat ~30 Field Sites
• Federal Sites– Hill AFB; Patrick AFB; Dover AFB; Vandenberg AFB;
Ft Lewis; Ft Devin; Indian Head; Port Hueneme; Paris Island; Cape Canaveral; Charleston; SRS; NASA
• Other Sites– Manufacturing Facilities in Indiana & Illinois – Dry Cleaner sites in Florida & Indiana
• International Sites– Borden CFB, Canada– Wales, UK– Australia (4 sites)
3
Four DNAPL Case Studies• Three large sites, one small site• Two source zones treated, one under
consideration• All sites had considerable archived data• At all sites new flux measurements made, PFM
deployments & Integral Pump Tests conducted• We will examine:
– Source & plume characterization– Source remediation performance assessment– Source & plume treatment options– Implications to long-term stewardship
4
DNAPL Site - 1
Patterson et al., EST 2006
MW46
-9-8-7-6-5-4-3-2-101
0 2 4 6 8qd (cm/day)
Elev
atio
n (m
AH
D)
0 2 4 6J(mg/m2/d)
q (cm/d) TriBE trans-DBE cis-DBE
MW47
-9-8-7-6-5-4-3-2-101
0 2 4 6 8qd (cm/day)
Elev
atio
n (m
AH
D)
0 25 50 75 100J(mg/m2/d)
q (cm/d) TriBE cis-DBE trans-DBE
MW22
-9-8-7-6-5-4-3-2-101
0 1 2 3 4 5qd (cm/day)
Elev
atio
n (m
AH
D)
0 2000 4000 6000J(mg/m2/d)
q (cm/d) TriBE cis-DBE trans-DBE
MW48
-9-8-7-6-5-4-3-2-101
0 2 4 6 8 10qd (cm/day)
Elev
atio
n (m
AH
D)
0 2000 4000 6000 8000
J(mg/m2/d)
q (cm/d) TriBE cis-DBE trans-DBE
MW24
-9-8-7-6-5-4-3-2-101
0 1 2 3 4 5qd (cm/day)
Elev
atio
n (m
AH
D)
0 100 200 300J(mg/m2/d)
q (cm/d) TriBE cis-DBE trans-DBE
Source Control Plane Fluxes
Unpublished Data: Do Not Cite or Distribute
6
Cross Section of Source Transect
MW46
MW47
MW22
MW48
MW24
q = 1-2 cm/day
q = 3-6 cm/day
2200
1500
2200
1700
660
4400
<1
48
<118
18
<1
<1
<1
Contaminant Fluxes are in mg/m2/day
<1
Mass Discharge:~ 38 kg/year
Unpublished D
ata: Do N
ot Cite or D
istribute
DNAPL Plume Mass• Plume mass (Mp) was estimated from integration of plume data (monitoring over 2002-2007 period)
• Most of the TriBE mass is found in the Intermediate aquifer
• Total mass of TriBE has stabilized at ~100-200 kg (additional mass in sorbed phase; R=??)
• Might be approaching “steady-state”conditions; stable plume??
• Need to consider mass of DBE, VB, Br.
Unpublished Data: Do Not Cite or Distribute
Patterson et al., EST 2006
Mass in Plume (kg)
8
Lessons Learned: DNAPL Site 1•Source mass: ~1.5-3 mT? (500-1,000L?)•Contaminant mass discharge from a small area of control plane
•Archived data integrated with flux data for an improved Conceptual Site Model
•Partitioning Inter-well Tracer Tests & Integral Pump Tests recently completed
•Aggressive source remediation & plume management planned
•Post-remediation monitoring to establish effectiveness & design long-term stewardship
HistoryTCE plume created due to activities associated with the production of detonators from the Second World to the 1970s
Hydrogeology• Multiple interconnected aquifers
• 4 quaternary aquifers and three tertiary aquifers
• v = 20 – 40 m/yr
• Water table ~ 10 to 15 m bgs
Plume Characterization• Plume monitored since 1996
•1,500 m long, 300 m wide and 16 m deep Remedial activities to dateShallow excavation in source area
Proposed Site RemediationChemical oxidation of source??
Permeable Reactive Barrier??
Remediation driven by:• Industrial redevelopment• Flexible regulatory environment• Cost constraints (passive vs aggressive)
DNAPL Site-2
MW 205
MW 227
MW 222
MW 18
MW 1
MW 225
MW 224
MW 223
MW 219
Plume Control Plane Wells
MW219
MW6
MW5B
MW5A
MW241
MW21810
15
20
25
30
35
0 20 40 60
length along transect (m)
dept
h bg
s (m
)Source Control Plane Wells
MW4A
MW4B
MW3AMW1A
MW1B
MW1C
MW2A
MW2B
MW3B
10
15
20
25
30
35
0 5 10 15 20 25
length along transect (m)
dept
h bg
s (m
)
10 μg/L
MW 221
MW 220
200 0 200 400 meters
TCE Plume with Monitoring Wells& Two Flux Control Planes
11
Source Transect Well
Plume Transect Well
13
16
19
22
25
28
31
0 2 4
qd (cm/day)
dept
h bg
s (m
)
0 50 100J(mg/m2/d)
• Source Strength = 3 g/day (other sites: 100 – 400 g/day)
• Negative Correlation
• Plume Strength = 6 g/day• Positive Correlation• No degradation
Basu et al., JCH 2008 (in review)
Well 241&218
13
16
19
22
25
28
31
0 2 4
qd (cm/day)
dept
h bg
s (m
)
0 50 100J(mg/m2/d)
q (cm/d)
J (mg/m2/d)
Clayey sand
Sandy Clay
Clay
Clay
TCE & Groundwater Flux Profiles:PFM Deployments
• Several small areas with conc >1500 ug/L • Plume disconnecting from a depleted source zone• Some shifts in plume shape• Decrease in source mass discharge
TCE Plume Dynamics
Source Mass Estimation
Method A:
( )( ) ( )2006 1996
1996
exp 10
exp 10d t
M M k
V AC k k=
= −
= −
Method B:
M2006 = present source mass
< 10 kg
,0,0
00
exp 2250t
DP D
MM M t dt kg
M⎛ ⎞
= − =⎜ ⎟⎝ ⎠
∫
,0, ,0
0
exp 1 /DD t D
MM M t kg year
M⎛ ⎞
= − =⎜ ⎟⎝ ⎠
M0 = 2,260 kg
MD,0 = 170–365 kg/yr
M2006 ~ 10 kg
14
Proposed Remediation at Site: Chemical Oxidation of SourceObservations
1. Source strength small compared to other sites (3 g/day)
2. Flux data indicate negatively correlated source distribution – high concentrations in low flow regions
3. Mass discharge at source and plume control planes of similar magnitude: plume degradation rates ~ 0
4. Source concentrations are decaying and will attain irrigation standards in <10 years
5. Source mass <10 kg, Plume mass ~ 3800 kg
Interpretations1. Source removal is not important
at this site??
2. Source treatment maybe inefficient due to accessibility of isolated ‘hotspots’
3. Plume remediation or containment is vital
4. Source removal is not important?
5. Plume remediation more important than source
Recommendations:
1. No source removal is necessary
2. Plume treatment or containment maybe required
Integration of Historic Data with Mass Flux Measurements
0 100 200 300 400
Feet
Area 1Area 2
Area 3
• TCE source zone delineated (three major zones: NA1, NA2, NA3)• Electrical Resistive Heating (TRS) of source zones• Measured mass flux using Passive Flux Meters (PFMs) and Integral Pump Tests (IPTs) -- before and after source treatment at NA1 & NA3
Ft Lewis, WA
16
Flux Transect Wells
NA1Source
Area
17
Hill AFB OU2HistoryCreated due to disposal of chlorinated solvents from degreasing operations during 1967 to 1975
Hydrogeology• Shallow unconfined aquifer
• K ~ 2 m/day
Plume Characterization• DNAPL pooled in the paleo-channel forming a source
• 900 m long, 150 m wide, and 10 m deep plume
Source Remediation Activities• 40,600 gallons DNAPL recovered
• In 1996 containment wall constructed around the source area
• In 1997, additional DNAPL discovered in a depression in the clay surface, just north of the containment wall in Panel 5.
• Study initiated to investigate effects of mass removal on mass discharge
• SEAR resulted in TCE mass depletion 1,300-2,200 kg; >70% reduction??
7 August 2003
Panel 5 Clay Aquitard SurfaceFigure 1
Operable Unit 2
Hill AFB, Utah
0
4
8
12
16
20
U2-154 U2-152 U2-150 U2-148 U2-116 U2-149 U2-151 U2-153
Well
Pre
TCE
Mas
s D
isch
arge
(g/d
ay)
0.0
0.4
0.8
1.2
1.6
2.0
Psot
TC
E M
ass
Dis
char
ge
(g/d
ay)
PrePost
0
0.5
1
1.5
2
2.5
3
1 2 3 4 5 6 7 8 9 10
Well ID
Pre
Mol
ar D
isch
arge
(m
oles
/day
)
0
0.05
0.1
0.15
0.2
0.25
0.3
Post
Mol
ar D
isch
arge
(m
oles
/day
)
PrePost
Field studies indicate significant decrease in mass discharge from source zones after DNAPL mass removal.
Effect of Source Remediation
Hill AFB Surfactant Remediation
Flux reduction >98%
Ft Lewis Thermal Remediation
Flux reduction >90%
Brooks et al. JCH In review
20
DNAPL Mass Depletion:Ft Lewis EGDY Thermal
NA1
NA2
NA3USACE, 2007 Draft Report
NA2
21
N
LC-213
LC-212
LC-211
LC-207
LC-206
LC-205
LC-204
LC-203
LC-202
LC-201
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
0.055
0.06
0.065
0.07
TCE Flux
(mg/cm2/hr)2313 332313 33
(Feet bgs)
Fort Lewis EGDY NA1
Pre-Remediation(Baseline GW Data)
USACE, 2007 Draft Report
Fort Lewis EGDY NA1
LC-213
LC-212
LC-211
LC-207
LC-206
LC-205
LC-204
LC-203
LC-202
LC-201
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
0.055
0.06
0.065
0.07
TCE Flux
(mg/cm2/hr)2313 332313 33
(Feet bgs)Thermal Treatment Cost ≈ $6M; Flux cost ≈ 2%
Peak-Thermal(Performance Monitoring)
USACE, 2007 Draft Report
USACE
April 2004
N
23
Lessons Learned: Ft Lewis EGDY• Detailed site characterizations required to locate and
delineate sources (cost & level of effort?)• Initial NAPL mass estimates; later revised with additional
analysis & interpretation.• Thermal treatment of NA1, NA2, NA3• ~2,600 kg TCE recovered during thermal treatment
(~70% reduction)• GW fluxes are large (q ~ 25 cm/day)• Thermal treatment reduced (>95%) TCE & DCE mass
discharge • Flux distributions across NA1 source control plane show
small area contributed most of mass discharge• How would the source remediation decisions have
changed if the flux distribution data were used?
24
Lesson Learned: Hill AFB OU2• TCE Mass discharge estimates using three
methods are in agreement.• TCE mass discharge is across a fraction of the
source control plane.• Source treatment (SEAR) resulted in TCE mass
depletion (1,300-2,200 kg removed; ~70% reduction) and an associated decrease (>90%) in TCE mass discharge.
• Increase in DCE mass discharge suggests increased biodegradation after SEAR.
• How does the source treatment influence plume evolution?
DNAPL Site Attributes
P&TNone?None?P&TPlume RemediationRecommendation
Flushing?None?ChemOx?ERH (99%+)Source Remediation
Site Management~10~1~0??Avg. Deg Rate Constant, k (yr-1)
~500~3,800~1,000~10,000Mass, Mp (kg)
250x50x151500x40x11500x120x155,000x500x50Dimensions(m x m x m)
Current Plume
30 x 10 = 30025x15 = 37510x5 = 5070x12 = 840Control Plane, Acp (m2)
~0.10.40?0.2Depletion Rate Constant, α (yr-1), α=[qAcpC0/M0]
~100~3~300~800Mass Discharge, MD, (g/day)
~150~570~10Max. Conc., Cmax (mg/L)
~2,500<100??~5,000Mass, m0 (kg)Current Source
5 (3 & 20)2.5 (1 & 13)10 (6 & 40)30Groundwater Flux, q (cm/day)
Site Hydrogeology
Oz-2Oz-1MidwestUS
NorthwestUSSITE PARAMETERS
REMChlor Simulations of Management Options
x ( m )
y(m
)
0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0-1 0 0
0
1 0 0t = 3 0 y e a rs
C o m p lia n c e B o u n d a ry
x (m)
y(m
)
0 1000 2000 3000-200
0
200 t = 60 yearsx(m)
y(m
)
0 500 1000 1500 2000 2500 30-200
0
200
50025055
TotalChlorinatedVOCs(ug/L)t=now
Plume shrinks at both ends Plume marches on at leading edgeBoth cases 90% mass depletion
SITE 1SITE 2
Control Plane
z
y
x
MD(t)
Total Chlorinated Solvents t=now
27
What Guides Remediation Choices?
1. Remedial ObjectivesCompliance boundary (“everywhere” or at specified POC?)Performance Metrics:
concentration or flux?Mass depletion & residual mass
Source and/or plume?2. Remediation timeframe
Short-term responsesLong-term site stewardship
3. Site CharacteristicsSource strength and longevityDegradation rates in the plume
Source Remediation Options?
MD (t) decreases over time (exponential?); so, if λ (t) is constant (?), eventually all plumes start shrinking–** requires long term stewardship for at least a century
1. No remediation
4.Integrated "Treatment Train" Approach: (2) + (3) → Implement "aggressive" short-term action to deplete most of the source mass (say, ~80%?), and then use the "passive" source treatment (nZVI or eZVI) to sustain essentially zero source flux, or a low-grade “chaser” of say chem ox
Plume response similar to 2; but, since the source mass hasn't been reduced, the source treatment has to be maintained for a very long time
3. Reduced Source Flux as in the case of n-ZVI or enhanced bio
Plume shrinks inwards from both ends
Plume “pinched off” at the head but tail continues to move forward –split plumes?
Plume “pinched off” at the head; tail starts shrinking when reduced MD reaches it
2. Reduce source mass through some aggressive source depletion action (e.g., flushing, chem ox, thermal, etc) MD(t) ↓
ShrinkingMD(t) < λ (t)
AdvancingMD(t) > λ (t)
StableMD(t) = λ(t)
options
29
Summary Comments• Groundwater & contaminant flux characterization
at DNAPL source control planes provides critical information needed in source remedy selection and performance assessment.
• “Source Strength” can be used to compare sites, and the required source strength reduction through mass depletion can be determined based on likely plume response.
• Regulatory framework and policy guidance lacking for adoption.
30
Discussion Items• How much longer will we debate the
benefits/limitations of partial mass removal for DNAPL source zones?
• If “MCL everywhere” can’t really be achieved “at reasonable cost and in reasonable time,” what are the alternatives for site remediation?
• If some DNAPL mass is left behind in the source zone, what are the implications to site stewardship (costs, risks, liabilities, etc)?
• How do short-term discounting procedures influence site remediation decisions at government & corporate sites?
31
Questions?