Research on Engineered Barrier Technology by

CRESP's Landfill Partnership

Craig H. Benson, PhD, PE, DGEWisconsin Distinguished Professor

University of Wisconsin-Madison/CRESPchbenson@wisc.edu

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W A S T E ACCESS

ROAD

On-Site Disposal Facility (OSDF):aka LLW or MW Landfill

FinalCover

System

LinerSystem

MONITORING

WELLS

Figure courtesy M. Othman, Geosyntec Consultants

The Challenge – Confident Design for a Millennium

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1 10 100 1000

Engi

neer

ing

Prop

erty

Time (years)

As-Built Current FieldResearch & Experience

?

?

?Analogs

Purpose of Landfill Partnership

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• Conduct independent applied research to address landfill technology issues that cross-cut the DOE complex.

• Provide forum to discuss regulatory conflicts and shortcomings, and to recommend technological solutions.

• Participate in independent technical reviews related to DOE technologies or sites.

Relevance

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• OSDFs (landfills) are key step in D&D/restoration at EM sites; stakeholder concerns regarding long-term performance impede acceptance/permitting.

• NAS (2009) identifies existing knowledge on long-term performance of waste containment structures as a principle science and technology gap for EM. Credibility gap for stakeholders.

• LP to provide source terms for EM’s ASCEM (analogous to CBP).

Technical Priorities to Build Confidence1. Develop confidence in the long-term (1000 yr)

performance of OSDF designs.2. Understanding of degradation mechanisms

affecting containment systems in OSDFs.3. Understand and quantify how final covers evolve

over the design life of OSDFs.4. Develop confidence in models used for PAs of

OSDFs and characterize uncertainty in predictions.5. Create and evaluate monitoring strategies that

build confidence in the performance of OSDFs.

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Approach to Build Technical Confidence• Understand our existing technology – does it

work as well as we predict?• Understand how barriers degrade or evolve

over time so that we can make confident long-term predictions.

• Develop reliable methods (e.g., computer tools) to predict performance in as-built state, and as barrier degrades.

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1. Understanding our Existing Technology

• State-of-the-art: knowledge base from field studies of barrier performance.– Resistive barrier technologies– Water balance barrier technologies

• State-of-the-art: lessons learned from field studies of cover soil pedogenesis.

• Leachate source terms for LLW disposal facilities.

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2. Developing Prediction Methods• Mechanistic description of radionuclide

sorption and diffusion in barrier systems.• Assessing methods to measure radionuclide

sorption and diffusion in barrier systems• Accounting for large-particle effects in soil

water retention.• Efficacy of transport models for predicting

transport through barrier systems.

• Evaluating how input uncertainty/sparseness affects uncertainty in model predictions.

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3. Understanding Barrier Degradation• Geomembrane degradation & life expectancy

in LLW facilities.• Degradation of bentonite barriers due to ion

exchange, hydration-exchange kinetics, and environmental stress (freezing, drying).

• Degradation of bentonite barriers exposed to concrete surfaces.

• Design strategies that manage degradation & ensure adequate performance (e.g., evolutionary covers, surface treatments).

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Speculative discussion at Paducah in March ‘11.

Literature suggests lifespan may be more than 1000 yr.

No data for conditions in LLW or MW facilities.

No credible scientific data for LLW or MW to draw inference, but

methods from solid waste literature

Geomembrane Degradation

Durability Tests in Synthetic LLW Leachate

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• Three temperatures (50, 70, & 90 C)

• Three solutions (DI, LLW, and LLW-Rad)

• 2 mm HDPE (ERDF, OSDF).

Parameters LLW

AverageSynthetic

Target

TOC (mg/L) 7.73 8

Reduction Potential (mV)

114.86 120

pH 7.21 7Inorganic Macrocomponents (mM/L) 

Calcium 3.71 4Magnesium 4.49 5

Sodium 5.27 5.6Potassium 0.38 0.5

Sulfate 7.11 7.5Chloride 4.7 5

Nitrate/Nitrite 1.42 1.5Alkalinity 3.42 3.5

Metals (mM/L)Aluminum 0.022 0.03

Arsenic 0.00066 0.001Barium 0.0017 0.002Copper 0.00011 0.0002

Iron 0.032 0.05Lithium 0.015 0.02

Manganese 0.0082 0.01Strontium 0.015 0.02

Zinc 0.0003 0.0005Radionuclides (ERDF Ave)

Uranium (µg/L) 1488 1500H-3 (pCi/L) 111530 120000

Tc-99 (pCi/L) 730 800

Geomembrane Incubators

Major Cations in LLW Leachate

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1x10-1

1x100

1x101

1x102

OSDF ERDF EMWMF ICDF All LLW MSW OSDF ERDF EMWMF ICDF All LLW MSW

Co

ncen

trat

ion

(m

mo

l/L)

Ca Mg(a) (b)

Radionuclides: U and Tc

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1x100

1x101

1x102

1x103

1x104

OSDF ERDF EMWMF ICDF All LLW

Co

ncen

trat

ion

of U

ran

ium

(µ

g/L

)

(a)

1x100

1x101

1x102

1x103

OSDF ERDF EMWMF ICDF All LLW

Co

ncen

trat

ion

of T

c-99

(pC

i/L)

(b)

Temporal Behavior: U and Tc

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1x100

1x101

1x102

1x103

1x104

0 2 4 6 8 10 12

OSDFERDFEMWMFICDF

Co

ncen

trat

ion

of

Ura

niu

m (

µg

/L)

Time (yr)

(a)

1x100

1x101

1x102

1x103

0 2 4 6 8 10 12

OSDFERDFEMWMFICDF

Co

ncen

trat

ion

of T

ech

netiu

m (

pC

i/L)

Time (yr)

(b)

Temporal Behavior: Sr and Tritium

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1x10-1

1x100

1x101

1x102

1x103

0 1 2 3 4 5 6 7 8

EMWMFICDF

Time (yr)

Co

ncen

trat

ion

of

Str

oni

um-9

0 (p

Ci/L

)

(c)

1x100

1x101

1x102

1x103

1x104

1x105

1x106

0 2 4 6 8 10 12

ERDF

EMWMF

ICDF

Co

ncen

trat

ion

of T

ritiu

m (

pC

i/L)

Time (yr)

(d)

Coupling Hydrological & Erosion Control on Covers

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631 m

631 m

807 m

452 m

Max Elevation = 1606 mMin Elevation = 1584 m

1606 m

1584 m

• Used Cheney Disposal Facility (Grand Junction, CO) as base case

• SIBERIA landform evolution model (1000 yr simulation)

• SVFLUX variably saturated flow model for hydrology.

Erosion on Rip-Rap Covers

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Resistive Cover Soil Profile

305 mm

150 mm

610 mm

610 mm

915 mm

Remaining

Cover top layer

Bedding layer (Rip-rap only)

Frost protection layer

Radon barrier

Transition layer

Tailings

1000 Year Erosion - Vegetated Riprap CoverSemi-Arid Climate

1 m2 m3 m4 m5 m6 m7 m

Rip-rap surface layer

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Resistive Cover Soil Profile

305 mm

150 mm

610 mm

610 mm

915 mm

Remaining

Cover top layer

Bedding layer (Rip-rap only)

Frost protection layer

Radon barrier

Transition layer

Tailings

1000 Year Erosion - Vegetated 40% Gravel Admixture CoverSemi-Arid Climate

2 m4 m6 m8 m

Gravel Admixture Topsoil Surface Layer

Coupling Hydrological & Erosion Control on Covers: Gravel Admixture Cover

Hydrological Prediction for Grand Junction, CO

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To

pso

il

Gra

ve

l A

dm

ixtu

re

Rip

-ra

p

To

pso

il

Gra

ve

l A

dm

ixtu

re

Rip

-ra

p

En

d-o

f-ye

ar

Cu

mu

lativ

e P

erc

ola

tio

n (

mm

)

-200

-100

0

100

200Typical Wettest • Gravel admixture

covers have net release to atmosphere

• Rip-rap covers harvest water – collect and drain into waste.

• Similar efficacy for erosion control!

FlowInto

Waste

FlowOut of Waste

Transport Parameters for Barriers

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Diffusion and sorption tests for geomembranes.

Evaluating new geomembrane with exceptionally low radon diffusion coefficient.

Transport Prediction for Barriers

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152 mm I.D.

Upper reservoir

Compacted clay linerGeomembrane

Effluent bagInfluent bag

Samplingport

Threaded tie-rod

120

mm

80 m

m

Sampling port

Glass fiber filter

30 m

m 3

0 m

m

60

mm

(a)

Sampling port

70 mm 12 mm 70 mm

Leachate

Geomembrane

Soil Liner

z = 0

Co Concentration

z

CsPartition out of geomembrane`Cg = Cs Kg

Partition intogeomembraneCg = Co Kg

Lg

Ls

Diffusion throughgeomembrane

Concentration distribution

Co= Leachate Concentration

Cg= VOC Concentration in Geomembrane

Cs= VOC Concentration in Soil Pore Water

Kg= Partition Coefficient of Geomembrane

Lg= Thickness of Geomembrane

Ls= Thickness of Soil Liner

Prediction - TCE Transport in Clay Barrier

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0

10

20

30

40

50

0 50 100 150 200 250 300 350 400

Replicate 1 (depth=60mm)Replicate 2 (depth=60mm)Replicate 3 (depth=60mm)Foose et al. (2002) (depth=60mm)POLLUTE (depth=60mm)Replicate 2 (depth=90mm)Foose et al. (2002) (depth=90mm)POLLUTE (depth=90mm)

Time (days)

Co

nce

ntra

tion

(mg

/L)

(c) TCE

Forward “Class A” predictions using independently measured input parameters (not calibrated)

Summary Remarks• Independent basic to applied research focused

on developing confidence in containment facilities.

• Focus on topics that our stakeholders indicate are important.

• Assess full-scale facilities and near full-scale demonstrations, understand fundamental mechanisms, and create/validate predictive models.

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