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Performance of Engineered Barriers: Lessons LearnedLessons Learned
Craig H. Benson, PhD, PE, NAE
Wisconsin Distinguished ProfessorUniversity of Wisconsin‐Madison/CRESP
1415 Engineering DriveMadison, Wisconsin 53706 USA
(608) 262‐[email protected]
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Barrier Systems for Waste Containment
Groundwater Gas collectionCover system
monitoring well
Waste
G d t
Native soil
Groundwater Leachate collection systemLiner system
Page 3
Challenges – Predicting the Futureg gerty ?
ng Prope
As Built ACAP
?
ngineerin As‐Built ACAP
Exhumations ?Analogs
En
1 10 100 1000Time (years)
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Conventional Resistive Covers with a Soil Barrier
GeosyntheticClay Liner
(GCL) Cover
CompactedClay Cover
• Performance controlled by saturated hydraulic
f( )
conductivity of clay barrier, either natural compacted clay or
Soil Soil
compacted clay or geosynthetic clay liner
CompactedClay
Waste • Install barrier to achieve hydraulic conductivity
W t
GCLgoal and protect barrier from damage that alters hydraulic conductivityWaste
4
hydraulic conductivity.
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Conventional Resistive Covers with a Composite Barrierp
GCL-GMComposite
Clay-GMComposite
• Performance controlled b t t d h d liCompositeComposite by saturated hydraulic conductivity of clay barrier and integrity of
Soil Soil
barrier and integrity of geomembrane.
Lif fCompacted
Clay
Waste
• Lifespan of geomembrane controls service life of coverClay
GCLGeomembrane(GM)
service life of cover.
• Current thinking 500-1 00Waste
(GM)
5
1500 yr.
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Alternative Water Balance CoversMonolithic
BarrierCapillaryBarrier • Performance controlled
b t t d dby saturated and unsaturated hydraulic properties of cover soils
FineTextured
FineTextured
Soil
properties of cover soils.
• Physically and bi l i ll tiTextured
SoilSoil biologically active
systems.CoarseSoil • Properties affected by
environment, “ d i ”Waste Waste
6
“pedogenesis.”
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Composite Liner
• Performance controlled by saturated hydraulicby saturated hydraulic conductivity of clay barrier and integrity of geomembrane.
• Lifespan ofLifespan of geomembrane controls service life of barrier.
• Impact of LLW on GCLs and geomembranes
7
and geomembranes unknown.
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1.5 mmLLDPELLDPE
Textured G bGeomembrane
8
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Geosynthetic Clay LinerLiner
9
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Focus for Today• Covers -- hydraulic
properties of soil barriers in ti l d tconventional and water
balance coverso Saturated hydraulico Saturated hydraulic
conductivityo Unsaturated hydraulic y
properties
• Liners hydraulic• Liners – hydraulic properties of GCLs & service life ofservice life of geomembranes in LLW
10
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Clay Barriers in CoversFactors affecting long-term performance include:• Cracks caused by wet-dry
cyclingC k d b f• Cracks caused by freeze-thaw cycling
• Cracks caused by• Cracks caused by differential settlement
• Biota intrusion• Long-term mineralogical
change
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Field Cover Performance:ACAP Lysimeters
20
Cover
InterimCover Soil
LLDPECutoff
RootBarrierLLDPE
Cutoff
LLDPEExisting Slope (>2%)
EarthenBerm
EarthenBerm
GeomembranePercolationPipe
Existing Slope (>2%)Geocomposite Drain
13
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Aerial view of completed test sections at Kiefer Landfill, Sacramento County, California.
14
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Borehole Test – Monticello U Tailings Repository
15
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Collecting Block Samples
16
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Preparing Blocks for Hydraulic Properties Tests
Block sample Trimming roughly to take ring‐off
Placing the block sample Trimming to the pedestal size
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Field Site in Albany, GA4000 250
3000
3500
nspi
ratio
n,(m
m)
Precipitation
2500
3000
200
Evap
otra
ner
cola
tion Soil W
a
Soil Water StorageDry Period
1500
2000
er A
pplie
d,
off,
and
Pe ter S
torage
1000
1500150
ativ
e W
ate
rface
Run
o e (mm
)
Evapotranspiration
0
500
100
Cum
ula
Su PercolationRunoff
0 1004/1/00 10/20/00 5/11/01 11/30/01 6/20/02 1/9/03 7/31/03
Percolation constituted 8.6% of precipitation before drought, 29.3% afterwards.18
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Field Hydraulic Conductivity Measurements on
Hydraulic
Clay Barrier - February 2004
TestHydraulic
Conductivity (cm/s)
Kf/Ko
As-Built 4.0x10-8 1.0
SDRI 2.0x10-4 5000
TSB - 1 5.2x10-5 1300
TSB 2 3 2x10-5 800TSB - 2 3.2x10-5 800
TSB - 3 3.1x10-3 77,500
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Rock Armor Covers – Cheney Field ExperimentsExperiments
R k Ri30 cm
Bedding Layer 15 cm
Rock Riprap
45 cm Protection Layer
Compacted Soil Layer(Rn Barrier)
45 cm
Tailings
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ECAP Test Sections at CheneyECAP Test Sections at Cheney
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Collecting Block Samples for Hydrologic PropertiesHydrologic Properties
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Evolution of Frost Protection Layer and Radon Barriers 2007‐13and Radon Barriers 2007‐13
10-3 Frost Protection Layer Radon Barrier • Hydraulic
10-4
vity
(cm
/s) conductivity of
frost protection and radon barrier
10-6
10-5
lic C
ondu
ctiv and radon barrier
increased, approx 10-7 cm/s
10-8
10-7
rate
d H
ydra
u approx. 10 cm/s as-built to 10-6
cm/s (10x)
10-9
10 8
FP As-Built FP 2013 RB As-Built RB 2013
Sat
ur
( )
• Preliminary, more testing currently
23
testing currently being conducted.
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Cheney Water Balance Datay1400 20
Cheney (R)
on,
Percolation
• Episodic percolation
1000
1200
15
vapo
trasn
pira
tige
(mm
)
Cum
ulative R
On-Site Precipitation
percolation indicative of macro-structure in
600
80010
pita
tion
and
Ev
Wat
er S
tora
g
Runoff and P
eSoil Water Storage
radon barrier and frost protection
200
400 5
mul
ativ
e Pr
ecip
and
Soi
l rcolation (mm
)
On-Site Evapotranspiration
layer.
• Performance still
0
200
010/31/07 11/9/08 11/20/09 11/30/10 12/11/11 12/20/12 12/31/13
Cum
)
Surface Runoff excellent, avg. percolation = 1.0
d 2 8 /24
and 2.8 mm/y
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Changes in Sat. Hydraulic Conductivity
If no change, data ld
10-5
10-4
s)
1:110:1100:11000:1(a)
would scatter around 1:1 line
10-6
10
rate
dty
, Ksi (m
/s
In-Service Hydraulic
Data coalesce into band with Ks = 10‐7
10-7
rvic
e S
atu
Con
duct
ivit Hydraulic
Conductivity
‐ 10‐5 cm/s independent of initial K9
10-8
AlbanyAltamontApple Valley
MonticelloOmahaUnderwood
In-S
eryd
raul
ic C
?
initial Ks
10-10
10-9
10 9 8 7 6 5 4
Apple ValleyBoardmanCedar RapidsHelena
UnderwoodPolsonSacramento
Hy
10-10 10-9 10-8 10-7 10-6 10-5 10-4
As-Built Saturated Hydraulic Conductivity, Ksa
(m/s)
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Effect of Climate100000
K sa Alterations in Ks10000
Rat
io, K
si/K Alterations in Ks
often assumed to be unique to drier
1000
nduc
tivity
R
qclimates.
Similar increases in
10
100
raul
ic C
on Similar increases in Ks for humid and sub‐humid
1
10
Sat
. Hyd
sub humid climates.
26Climate
Humid and Sub-Humid Arid and Semi-Arid
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Caisson Lysimeters – Monticello, UT
11 mFine
TexturedSoilBill Albright Soil
0 3
Bill Albright
0.3 mCobble& Soil
0.3 mSand
0.3 m0.3 mClayRadon 27
Eric MacDonald
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Radon Barrier – Monticello, UT
Roots seek out waterout water in wet fine‐
dgrained soils, e.g., clay radon barriers, ,even at 1.6‐1 9 m1.9 m depth
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Unsaturated Hydraulic Properties – Soil Water Characteristic CurveWater Characteristic Curve
0.50
In ServiceSoil becomes less
0.40
nten
t
dense (higher porosity or saturated water
t t) d h0.30
Wat
er C
on As-Built content) and has broader distribution of pore sizes
0.20
Vol
umet
ric of pore sizes.
Impact on water storage and
0.10
V storage and percolation depends on site specific
29
0.00100 101 102 103 104 105 106
Matric Suction (kPa)
on site specific conditions.
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Geosynthetic Clay Liners• For low hydraulic
conductivity, Na-Typical CrossTypical Cross--SectionSection
bentonite granules must swell to from a gel (paste).(p )
• Gel must be maintained to retain low hydraulic LowerLowerUpperUpper GranularGranularto retain low hydraulic conductivity (~ 10-9
cm/s) .
LowerLowerGeotextileGeotextile
UpperUpperGeotextileGeotextile
GranularGranularBentoniteBentonite
• If granules do not swell and form gel, higher h d li d ti ithydraulic conductivity (>10-9 cm/s).
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Hydraulic Conductivity of Exhumed GCLs
• Strong relationship with10-4
Lower KHi h K Strong relationship with
water content
• Transition point lower, y (c
m/s
)
10-6
10-5Higher K
p ,but sufficient water for osmotic swell (> 50%)
Con
duct
ivity
10-7
• Rapid and sufficient hydration yield low hydraulic conductivityH
ydra
ulic
C
10-8
hydraulic conductivity
20 40 60 8010-10
10-9
31Exhumed Gravimetric Water Content (%)
20 40 60 80
Page 32
250
Exhumed Water Content
200
250
%)
150
200
Con
tent
(%
100
150
d W
ater
C
Composite GCL GCL-only
50
100
Exhu
med
0
50
0A B E-01 E-02 F-03 F-05 S D N O
Site
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Cover Exhumation at LLW Disposal Site in Southeastern USA
600 mm surfacelayer
30 cm sand drainage layerlayer
1.5 mm geomembrane
GCL
300 mm low hydraulic
Foundation layer
300 mm low hydraulic conductivity soil layer
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Hydraulic Conductivity of GCLsHydraulic Conductivity of GCLs
Sample Water Content Hydraulic ConductivitySample(%) (cm/s)
GCL1a 112.2 9.6x10‐10
GCL1c 115.0 8.6 x10‐10
GCL2a 110.4 9.5 x10‐10
GCL2c 119 6 7 0 10 10GCL2c 119.6 7.0 x10‐10
GCL3a 102.6 8.6 x10‐10
GCL4a 129 4 9 0 x10‐10GCL4a 129.4 9.0 x10 10
GCL4b 151.5 8.6 x10‐10
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Hydraulic Conductivity of Soil BarrierSample Sampling Location Condition
Gravimetric Water Content
(%)
HydraulicConductivity
(cm/s)
y y
( ) ( / )
BS1Away from Distortion
No cracks 15.2 2.2×10‐5
BS2Away from Contains small
16 0 1 5×10‐5BS2Distortion cracks
16.0 1.5×10
BS3Middle of Distortion
Contains large crack, GCL overlay
ND 8.4×10‐8
overlay
BS4Immediately
Below DistortionNo cracks 13.2 4.7×10‐5
BS5Away from Distortion
No cracks 14.0 1.1×10‐5
BS6 Top of DistortionContains large
14.0 3.0×10‐4
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BS6 Top of Distortioncrack
14.0 3.0×10
Notes: ND = not determined. Specimens fragile due to cracks.
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Composite Liner
• Performance controlled by saturated hydraulicby saturated hydraulic conductivity of clay barrier and integrity of geomembrane.
• Lifespan ofLifespan of geomembrane controls service life of barrier.
• Impact of LLW on GCLs and geomembranes
39
and geomembranes unknown.
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Accelerated Geomembrane Testing
• Immersed at 25, 50, 70, d 90 °Cand 90 °C
• Synthetic LLW leachate with (RSL) and withoutwith (RSL) and without (NRL) radionuclides 40
Page 41
LeachatesMajor Cations/Anions (mM) Trace Metals (mM)
Ca 4 As 0.001 Al 0.03
Mg 6 Ba 0 002 Mn 0 01Mg 6 Ba 0.002 Mn 0.01
Na 7 Cu 0.0002 Ni 0.0003
K 0.7 Fe 0.04 Sr 0.02
Sulfate 7.5 Li 0.02 Zn 0.0005
Cl 8 Chemical Characteristics
Nitrate 1.5 TOC (mg/L) 85 mg/L
surfactantNitrate 1.5 TOC (mg/L) 8
Alkalinity 3.5 ORP (mv) 120
Radionuclides pH 7.2
surfactant and 3 mg acetate
U‐238 (µg/L) 1500 Ionic Strength (mM) 43.6
H‐3 (pCi/L) 120000 Ratio of monovalent to divalent cations (M1/2)
( l d l )0.077
Tc 99 (pCi/L) 800 (Kolstad et al. 2004)Tc‐99 (pCi/L) 800
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Antioxidant Depletion in Geomembranes
250(a)
me
(min
) 200
n In
duct
ion
Tim
100
150
RSL-25 RSL 50
Oxi
datio
n
50
RSL-50 RSL-70 RSL-90
Time (month)
0 2 4 6 8 10 12 14 160
( )
42
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• AntioxidantService Life Predictions
1600
1800
DI (Immersion Test)
Antioxidant depletion in approx. 700 yr,
me
(yea
rs)
1200
1400NSL (Immersion Test) RSL (Immersion Test) RSL (Composite Liner)
first degradation phase.
plet
ion
Tim
800
1000
1200
Representative field
• Actual lifespan longer;
oxid
ant D
e
600
800 Representative field temperature 15 °C
ginduction & polymer
id ti
Ant
io
200
400 oxidation phases, 1000-1500 yr
Temperature (°C)
10 20 30 40 500 1500 yr.
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GCLs in Synthetic LLW Leachatey
10-9 3
10-10 2vity
(m/s
)
10 2
c C
ondu
citiv
C ti l b t it GCL10-11 1
Hyd
raul
ic • Conventional bentonite GCLs• Polymer‐modified bentonite GCLs• Bentonite‐polymer composite GCLs
10-12
0 10 20 30 40 50 600
Pore Volumes of Flow
44
Pore Volumes of Flow
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Impact of Radionuclides10-9
C1C2m
/s) • Essentially the
same hydraulic
10-10
C2
R1
R2BPCed
to R
SL (m
2x
same hydraulic conductivity with or without
tivity
Exp
ose
2x
2x or without radionuclides in leachate.
10-11
aulic
Con
duct 2x
• Major cations control swelling
10-12
10-12 10-11 10-10 10-9
Hyd
ra control swelling and hydraulic conductivity.
45
10 10 10 10Hydraulic Conductivity Exposed to NSL (m/s)
y
Page 46
Impact of LLW Leachate on H dra lic Cond cti it of GCLs
10-9
Open= GCL exposed to RSLS lid GCL d t NSL Hydraulic Conductivity
Hydraulic Conductivity of GCLse
(m/s
)
100 x
Solid = GCL exposed to NSL Hydraulic Conductivity Relative to DI Water
C ti l10-10
vity
to L
each
ate
2 x
5 x
10 x
• Conventional bentonite: ~ 100x
10-11 C1
C2aulic
Con
duct
iv 2 x• Polymer‐modified
bentonite: ~ 10xC2
R1
R2
BPC
Hyd
ra
• Composite: ~ 2x
46
10-12
10-12 10-11 10-10 10-9
Hydraulic Conductivity to DI Water (m/s)
Page 47
Conclusions: Soil Barriers & GCLs in Covers
• Soil barriers undergo pedogenesis, altering their hydraulic properties Plan for this intheir hydraulic properties. Plan for this in design and account for long‐term properties in PAin PA.
• Impact of changes on performance highly site f f b l fspecific, from substantial to insignificant.
Avoid generalizations about impact.
• Changes occur in all climates (not just arid), and occur at depth. Depth dependence is an issue requiring more study.
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Conclusions: Soil Barriers & GCLs in Covers
• GCLs can maintain very low hydraulic conductivity in covers even with cationconductivity in covers even with cation exchange if they are adequately hydrated initially and they are protected frominitially and they are protected from desiccation.
d h h b d• GCLs and other geosynthetics can bridge distortion due to differential settlement.
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Conclusions: Liners• Impact of LLW leachate on geomembranes and GCLs is due to primary cations and metals in solution. Radionuclides not important from perspective of degradation.
• Geomembrane service life at least 700 yr, probably > 1000 yr when all three phases p y y pconsidered.
• GCLs are more permeable in LLW leachates thanGCLs are more permeable in LLW leachates than to water and other more common leachates (e g solid waste) Can address with polymer(e.g., solid waste). Can address with polymer modified bentonites. Account for in PA. 49