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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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)
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
High tip heads can create:
coarser layers/zones conducive
for oxygen transport (advective
flow)
preferential flow paths for water
long-term closure liability ($$$$)
Internal Construction– High Tip Heads
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
High tip heads can create:
coarser layers/zones conducive
for oxygen transport (advective
flow)
preferential flow paths for water
Shorter tip heads can:
reduce potential for particle
segregation
help mitigate the formation of
advective cells (compacted layers
and starter bunds)
However, higher placement cost
─ But SAVE $$$$ in the long-term
─ Site relinquishment possible
Internal Construction– Short tip heads
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
Internal Construction– Integrated WRD Assessment Method (Dumpsim)
Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology
Inc
rea
sin
g S
ulfu
r
Increasing Cost
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
WRSF Design for Closure
O’Kane Consultants (OKC) are taking a
“Quantitative Approach” to waste storage facility
design that incorporates:
Internal construction
External construction
(geometric design)
Cover system design
Performance
monitoring
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
Site LandformFailure Modes – Recent Examples
Long Steep Slopes
Bench and berm configurations
Erodible Materials
Run-on management
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
WRSF Design for Closure
O’Kane Consultants (OKC) are taking a
“Quantitative Approach” to waste storage facility
design that incorporates:
Internal construction
External construction
(geometric design)
Cover system design
Performance
monitoring
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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)
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
Net Present Value
Two breakeven points
─ Year 8 including alkalinity derived from CKD
─ Year 25 excluding alkalinity derived from CKD
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
Conclusions
Alkaline covers generate significant alkalinity
Relatively short period to break even compared
to treating acid in perpetuity
Site and material specific assessment required
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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:
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
N
Passive Treatment to Manage Residual
SeepageSurface
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
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.
Integrated Mine Waste Management and Closure Services
Specialists in Geochemistry and Unsaturated Zone Hydrology
O'Kane Consultants
Rainbow of Hope for Children and,
Habitat for Humanity Initiative
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