Planning for Closure:Field and Laboratory

Investigations forSoil Cover Design

Peter E. Kowalewski

SRK Consulting

Objective of Cover Design

• Obtain cover design that meets site’sobjective� Infiltration-limiting� Oxygen-limiting

• Obtain estimate of long term soil coverperformance� Quantify percolation through covered ore� Identify risks with regard to cover stability

Idealized Approach

• Conceptual/Preliminary Design� Types of covers to be evaluated

� Estimated soil types based on site knowledge

• Site Soils Investigation

• Numerical modeling of cover alternatives

• Establishment of test plots / Monitoring

• Validation of numerical model

• Selection of preferred cover alternative

• Construction

Overview of Data Requirements

• Climatic Data� Site-specific

• Soils Data� Ore to be covered

� Potential cover soils

Quantifying Cover Performance

• Predictive Numerical Modeling� SoilCover, HYDRUS 1-D/2-D, SEEP/W, etc…

• Field Demonstration� Instrumented Cover Test Sections

• Tensiometers• TDR• Moisture Sensors• Soil Water Potentiometers• Lysimeters

Field Demonstration - Benefits

• Provides data related to actual coverperformance (vs modeled results)

• Allows cover model to be verified� Provides degree of reliability to long term

performance predictions

• Allows for identification of potential costsavings in design

Site Soils Investigation

• Identify potential sources of cover soils� Identify available soil volumes

� Assess geotechnical properties

� Establish range of properties

• Assess properties of ore to be covered� Operational and closure task

Ore Investigation

• Assess/confirm geotechnical properties

• Identify in-situ conditions of ore� Variation in profile?

• Density

• Moisture content

• Saturated Permeability

Cover Soil SWCC Comparison

0

0 .05

0 .1

0 .15

0 .2

0 .25

0 .3

0 .35

0 .4

0 .45

0 .5

0 .01 0 .1 1 10 100 1000 10000

Suction (kPa)

Vol

. Moi

stur

e C

onte

nt (%

)

Cover Soil SWCC Comparison

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.1 1 10 100 1000 10000

M a tric Suction (kPa )

Moi

stur

e C

onte

nt (v

ol %

)

Barrier Soil SWCC Comparison

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.01 0.1 1 10 100 1000 10000

Suction (kPa)

Wat

er C

onte

nt (v

ol %

)

Ore SWCC Comparison

0

0 .05

0 .1

0 .15

0 .2

0 .25

0 .3

0 .35

0 .4

0 .45

0 .5

0 .01 0 .1 1 10 100 1000 10000

Suction (kPa)

Vo

l. M

ois

ture

Co

nte

nt (

%)

P -1 5 P -1 2 5 P -1 9 4 P -2 9 P -2 5 9 P -2 6 8 .5 P -2 1 1 9 P -3 6 .5

P -3 2 9 P -3 9 3 .5 P -3 1 0 8 .5 P -3 1 2 2 L ite ra tu re L ite ra tu re

Heap Moisture Profiles

0

20

40

60

80

100

120

140

0.0% 5.0% 10.0% 15.0% 20.0%

Dept

h (ft

)

Note: V olumetr ic Mois ture Contents

0

20

40

60

80

100

120

140

160

0.0% 5.0% 10.0% 15.0% 20.0%

0

20

40

60

80

100

120

140

160

0.0% 5.0% 10.0% 15.0% 20.0%

Conclusions

• Benefits� Site-specific data included in analyses

� Optimized cover design

� Validated cover performance

� Potential capital cost reduction