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) 262‐7242chbenson@wisc.edu

Barrier Systems for Waste Containment

Groundwater Gas collectionCover system

monitoring well

Waste

G d t

Native soil

Groundwater Leachate collection systemLiner system

Challenges – Predicting the Futureg gerty ?

ng Prope

As Built ACAP

?

ngineerin As‐Built ACAP

Exhumations ?Analogs

En

1 10 100 1000Time (years)

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.

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.

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.”

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.

1.5 mmLLDPELLDPE

Textured G bGeomembrane

8

Geosynthetic Clay LinerLiner

9

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

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

11

CracksCracks

12

Field Cover Performance:ACAP Lysimeters

20

Cover

InterimCover Soil

LLDPECutoff

RootBarrierLLDPE

Cutoff

LLDPEExisting Slope (>2%)

EarthenBerm

EarthenBerm

GeomembranePercolationPipe

Existing Slope (>2%)Geocomposite Drain

13

Aerial view of completed test sections at Kiefer Landfill, Sacramento County, California.

14

Borehole Test – Monticello U Tailings Repository

15

Collecting Block Samples

16

Preparing Blocks for Hydraulic Properties Tests

Block sample Trimming roughly to take ring‐off 

Placing the block sample  Trimming to the pedestal size 

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

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

19

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

ECAP Test Sections at CheneyECAP Test Sections at Cheney

Collecting Block Samples for Hydrologic PropertiesHydrologic Properties

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.

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

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)

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

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

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

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.

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).

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

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

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

33

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

37

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

38

BS6 Top of Distortioncrack

14.0 3.0×10

Notes: ND = not determined. Specimens fragile due to cracks.

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.

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

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

41

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

• 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.

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

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

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)

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.

47

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.

48

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