Andre Kemp - O'Kane Consultant

Integrated Mine Waste Management and Closure Services

Specialists in Geochemistry and Unsaturated Zone Hydrology

Andre Kemp: General Manager Western Australia

Mining the Territory

15th September 2016

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Mine Waste Landform Design



Presentation Overview

Key rehabilitation strategy goals

Re-designing reactive waste landforms to achieve

both geochemical and geotechnical long-term

stability

Reducing long-term risk and financial liability

through improved planning and construction



Key Rehabilitation Strategy Goals

Environmental

─ Safe

─ Stable

─ Non polluting

─ Ecologically sustainable

─ Support sustainable land uses by Aboriginal owners

─ Encourages beneficial alternative post-rehabilitation

land uses

Corporate

─ Financially viable

─ No long-term financial liability



How do we do it “Better”

Setting and communicating closure goals

(overarching objectives)

Develop site-specific closure objectives

Design criteria from objectives

Complete a design that meets these criteria

Develop performance criteria (from all above)



Alternative Approach

“what is the shortest haul to place waste?”

to…

“meet mine scheduling requirements at lowest cost?”

OR:

“minimise long-term environmental risk from AMD”

How can we make it a Question of AND not OR?

o “Maximising grade of ore while minimising haul

AND minimising discounted costs of waste rock

construction and management”

The “Current Question” at most sites:

At the very least we should strive to improve our

understanding when we can’t change dumping practices



WRSF Design for Closure

O’Kane Consultants (OKC) is taking a “Quantitative

Approach” to waste storage facility design that

incorporates:

Internal construction

External construction

(geometric design)

Cover system design

Performance

monitoring



WRSF Design for Closure– Why a Quantitative Approach?

In General… Five Variables that Influence AMD Risk

3) Physical characteristics

2) Sulfide content

4) Structure / Placement method1) Climate

5) Cover and treatment



Geochemical Classification using

Process Flow Material Characterisation Minimised and optimised testing

─ Matrix style classification (A)

• 2,904 individual tests (assuming 4 tests per sample)

• 35% successful classification (726 sample database)

• 23% insuff. data due to phasing out old testing regime

─ Process flow classification (B)

• 1,514 individual tests

• 98% successful classification (726 sample database)

ABA database sample classification by the (A) matrix style and (B) process flow approach



Test cost Process Flow Matrix style

$/analysis No. tests Cost No. tests Cost

Total S $20.00 726 $14,500.00 726 $14,500.00

NAG pH $35.00 430 $15,100.00 726 $25,400.00

ANC $45.00 179 $8,100.00 726 $32,700.00

Sulfide S $35.00 179 $6,300.00 - -

Paste pH $15.00 - - 726 $10,900.00

Total - 1514 $44,000.00 2904 $83,500.00

Process Flow - Escarpment

Indicative testing cost comparison (726 sample database)

─ Process flow classification – ~ $44 k for 98% classification

─ Matrix style classification – ~ $84 k for 35% classification

NB: test cost ($/analysis) indicative only



High tip heads can create:

coarser layers/zones conducive

for oxygen transport (advective

flow)

preferential flow paths for water

long-term closure liability ($$$$)

Internal Construction– High Tip Heads



High tip heads can create:

coarser layers/zones conducive

for oxygen transport (advective

flow)

preferential flow paths for water

Shorter tip heads can:

reduce potential for particle

segregation

help mitigate the formation of

advective cells (compacted layers

and starter bunds)

However, higher placement cost

─ But SAVE $$$$ in the long-term

─ Site relinquishment possible

Internal Construction– Short tip heads



Internal Construction– Quantitative Approach?

OKC Analytical model that has algorithms to determine:

1. Internal heating of waste

2. Contaminant production

3. Seepage rate (and acid load)

4. Gas generation (e.g. CO2)

Produces numerical output

so waste placement

techniques can be

compared quantitatively

For Example: How much less acid do we get if we end tip at

5m vs 30m?Pearce et al 2015

How do we quantify/estimate WRSF seepage

quality and quantity



Internal Construction– Is it worth it?

Cu

mu

lati

ve

Acid

ity (

t H

2S

O4)

Years0 20 40 60 80 100

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Acidity Produced

Acidity

Mobilised

Acidity Released

(toe/basal seepage)

Acidity Stored

End of Mining and cover

waste from this point forward

Pearce et al 2015



Internal Construction– Is it worth it?

Cu

mu

lati

ve

Acid

ity (

t H

2S

O4)

Years0 20 40 60 80 100

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Acidity Produced

Acidity

Mobilised

Acidity Released

(toe/basal seepage)

Acidity Stored

End of Mining and cover

waste from this point forward

Pearce et al 2015

Cu

mu

lati

ve

Acid

ity (

t H

2S

O4)

Years0 20 40 60 80 100

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Acidity Produced

Acidity

Mobilised

Acidity Released

(toe/basal seepage)

Acidity Stored

Economic benefit

with reducing

acidity production

and storage?Reduce stored acidity

Pearce et al 2015



Internal Construction– Integrated WRD Assessment Method (Dumpsim)


Inc

rea

sin

g S

ulfu

r

Increasing Cost



Internal Construction– Waste Scheduling

Waste Scheduling

Can often be a fatal flaw for WRD construction.

Need to know required materials for specific design

functions are available when needed




Internal Construction– Internal WRSF Monitoring

Monitoring Controls of AMD

Production / Release

Gas monitoring (O2 & CO2)

─ Oxidation rates

─ Oxygen ingress

Temperature

─ Indication of oxidation

process

─ Advective oxygen ingress

Hydrology

─ Response to rainfall

─ Seepage prediction




O’Kane Consultants (OKC) are taking a

“Quantitative Approach” to waste storage facility

design that incorporates:



(geometric design)

Cover system design

Performance

monitoring



Site LandformFailure Modes – Recent Examples

Long Steep Slopes

Bench and berm configurations

Erodible Materials

Run-on management




O’Kane Consultants (OKC) are taking a

“Quantitative Approach” to waste storage facility

design that incorporates:



(geometric design)

Cover system design

Performance

monitoring



Alkalinity Generating Covers

Further benefits from acid base accounting

perspective

─ Alkaline percolation → 90 % reduction in sulphide oxidation

(Smart et al 2010).

Cement Kiln Dust (CKD)

─ By-product of cement manufacture

─ Acid neutralising capacity (~ 650 kg CaCO3 eq./t)

─ Paste pH ~11-13

─ ANC of CKD primarily as relatively soluble oxides

─ Fine material offering low permeability properties

─ Elevated in thallium (Tl)



Net Present Value

Two breakeven points

─ Year 8 including alkalinity derived from CKD

─ Year 25 excluding alkalinity derived from CKD



Conclusions

Alkaline covers generate significant alkalinity

Relatively short period to break even compared

to treating acid in perpetuity

Site and material specific assessment required



Cover System: Delay Treatment

─ Covers an area of 26 ha

─ Height of 40m

─ Plateau ~7%

─ Side Slope 3:1

─ Runoff ditch constructed

around plateau which

channels runoff to drop

structures on side slope

Landform:



N

Passive Treatment to Manage Residual

SeepageSurface



1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

2011

2013

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Progressive changes to

site operations:• Factors leading to changes

in loading and water quality

Dev. Conceptual Model

Acid Load Mass

Balance to Test Two

Conceptual Models:1) Active treatment no

cover system

2) Passive treatment

with cover system

1 2



Oxygen Flux Net Percolation

30-40 m

Oxygen 21%, Decreasing With DepthHigh Net Percolation ~350 mm/yr

PAF Waste Rock 788 t/yr

19 t/yr

273 t/yr

132 t/yr

656 t/yr

158 t/yr

3 t/yr

MP2016Net Percolation

Runoff From Site

Active Treatment System

Mounding Pump/Treat

Calculated = 161 t/yr

Observed = 150 t/yrError = 1% 937t / 948t

Groundwater

Alkalinity

-2 t/yr

160 t/yr

1) No Cover System w/ Active

• Pump/treat: flow and concentration available

(Pump/treat includes wet well, pump / treat wells and toe drain)

• Water treatment facility: lime usage, flow, and concentration

• Net percolation: flux and source term

Source term, water quality

at base of pile

RO: 70%

P/T: 45% of basal loadTotal: 950 t/yr

Total: 150 t/yr



2) Cover System w/ Passive

Oxygen Flux Net Percolation

0.4 m Runoff From Site1.52 mm

Drain-down

Net Percolation

0.4 m Till Growth Medium Cover Layer

Granular Drainage layerHDPE Geomembrane

30-40 m

Oxygen < 1%, Decreasing With DepthLow Net Percolation ~4 mm/yr

PAF Waste Rock0 t/yr

Leachate Collection System

Passive Treament System

MP2016

10 t/yr

2 t/yr

19 t/yr0.5 t/yrMounding

59 t/yr70 t/yr

10 t/yr

Calculated = 69 t/yr

Observed = 66 t/yrError = 4%

Alkalinity

Groundwater

Alkalinity

-2 t/yr

68 t/yr

Outcomes from Acid Load Mass Balance• Total acid load reduced from ~948 t/yr to 80 t/yr

• Context for 90% reduction in loading but only 44% at MP2016 Decommissioned pump-and-treat and wet bore, reduction in treated load

from 132 t/yr to 10t/yr

Approximately 12% of load collected in leachate collection system (LCS)

• Testing and refinement of the geochemical model

~45% reduction~90% reduction



Costs and Loading… and Risk

Discount Rate (%)

Collection and

Treatment

NPV

Cover System

NPV

1.0 $ 29.5M $ 16.1M

2.5 $ 17.0M $ 14.6M

4.0 $ 11.2M $ 13.8M

Pump and Treat System only Captured: 45% of basal load



Getting Back to the Question…

Can we limit operational costs and reduce long-

term liability by understanding waste better and

managing it accordingly

We can when;

Waste is well characterised (physical and

geochemical)

AMD potential is quantified

Appropriate (cost effective) placement methods are

applied based on the above



OKC Published Work

Recent published articles:

Kemp, A., Taylor, I. & O’Kane, M. 2016. Waste landform cover system and geometrical design – integration with

waste placement and landform optimisation approach. Mine Closure 2016

Kemp et al., 2014, Landform Design for Pilbara Mine Site - Why Plan and Design Waste Rock Dumps for Closure

Based on Site-Specific Conditions?

Pearce and Barteaux, 2014, Instrumentation of waste rock dumps as part of integrated closure monitoring and

assessment, Mine Closure 2014, Brisbane.

Pearce et al., 2014, Heterogeneity Profiling: A Technique to Improve Geochemical Sampling and Analysis for AMD

Assessments, Eighth Australian Workshop on Acid and Metalliferous Drainage 2014, Adelaide.

Pearce and Gutierrez, 2015, Opportunistic AMD Sampling from Multi-Discipline Drilling Programs for Large Mining

Companies, 10th International Conference on Acid Rock Drainage 2015, Santiago.

Pearce et al., 2015, Advanced Customisable Leach Columns (ACLC) – A New Kinetic Testing Method to Simulate

Site-specific Conditions, Tailings and Mine Waste Management for the 21st Century 2015, Sydney.

Pearce et al., 2015, Quantitative Risk Assessment Tools to Assist with Waste Management and Placement

Guidelines, AusIMM 2015, Sydney.

Taylor et al., 2014, Defining effective closure and reclamation measures for tailings and waste rock storages: an

African case study.

Taylor et al., 2014, Building better waste landforms for reactive waste: a new level of waste assessment and

construction.

[email protected]



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Andre Kemp - O'Kane Consultant