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Whistle Mine: Design, Construction and Performance Monitoring of thePit Cover and Impacts on Water Treatment
Lisa Lanteigne, P.Eng.Senior Specialist - EnvironmentSudbury Operations
Presentation Outline
• Background• Cover System Design• Final Landform Design• Sustainability of the
Cover and Final Landform
• Construction of the Pit Cover• Performance of the Pit Cover• Evolution of Water Treatment• Concluding Remarks
Background
• Canadian Shield –numerous bedrock outcrops and lakes
• Open pit mining (nickel) between 1988-91 & 1994-98
• 6.4 Mt of waste rock on surface – 80% was mafic norite, avg. S of 3%
• Semi-humid climate –annual precip. of 900 mm (30% as snow) & potential evaporation of 520 mm
Background
• Several acidic seeps developed
• Collection ponds were excavated as seeps were discovered
• Water management was a challenge –inadequate storage capacity
• Environmental spill in 1999
Background
• Not feasible to reclaim WRDs in-place
• Based on available data, Inco decided to relocate all waste rock to open pit (with lime addition @ 2kg/tonne) and cap with an engineered cover
• Pit cover area ~10 ha• Objectives of cover system:
1) Limit oxygen ingress2) Reduce water infiltration3) Growth medium for vegetation
~7H:1V
Cover Design: Approach
Cover System Field Trials
Geochemical Modeling
Selection of Barrier Layer Material
Soil-Atmosphere Cover Design Modeling
Erosion and Landform Evolution Modeling
Slope Stability Analysis
Consideration of Processes Potentially Impactingon Sustainable Performance
CoverDesignCriteria!
Cover Design: Preliminary Modeling Results
Barrier Layer Thickness
Growth Medium Layer Thickness Simulation
Barrier LayerDeg of Saturation
30 cm 90 cmInitial conditions 90%
Dry year – run 1 78%
45 cm 90 cmInitial conditions 92%
Dry year – run 1 82%
60 cm 90 cm
Initial conditions 93%
Dry year – run 1 85%
Dry year – run 2 78%
30 cm 120 cmInitial conditions 93%
Dry year – run 1 83%
45 cm 120 cm
Initial conditions 98%
Dry year – run 1 94%
Dry year – run 2 90%
Dry year – run 3 86%
Cover Design: Detailed Modeling Results
1 x 10-14
1 x 10-12
1 x 10-10
1 x 10-8
1 x 10-6
1 x 10-4
1 x 10-2
1 x 100
0 50 100 150 200 250 300 350 400Distance (m)
Oxy
gen
diffu
sion
coe
ffici
ent (
m2 /
s)
-30
-20
-10
0
10
20
30
40
Ele
vatio
n (m
)
North South
Topography
Required Minimum O2 Diff. Coeff.for Barrier Layer
Final Barrier LayerO2 Diff. Coeff.
Initial Barrier Layer O2 Diff. Coeff.
Cover Design: Constructed Profile
LevellingLevelling CourseCourse
Growth Medium / Growth Medium / Protective LayerProtective Layer
Barrier LayerBarrier Layer
Waste RockWaste Rock
• Non-compacted sandy-gravel till
• 120 cm minimum on slope, with8 cm of topsoil admixed to the near surface material
• 60 cm minimum in the ponds
• Compacted Copper Cliff clay
• 45 cm minimum on slope
• 60 cm minimum in the ponds
• Non-compacted sandy-gravel till (~ 10 cm thick)
Landform Design: Output from Model (after 100 yrs)
Significant Gully / Rill Development and
Interill Erosion
Sustainability of Soil Covers
INITIAL PERFORMANCE
LONG-TERM PERFORMANCE
Chemical ProcessesPhysical Processes
- Erosion- Slope Instability
- Consolidation/Settlement- Extreme Climate Events- Brush Fires- Construction
- Wet/Dry Cycles- Freeze/Thaw Cycles
- Root Penetration- Burrowing Animals- Bioturbation- Human Intervention- Bacteriological Clogging- Vegetation Establishment
- Osmotic Consolidation- - Dissolution/- - - Sorption- Salinization- Oxidation
Dispersion/ErosionPrecipitation
Acidic HydrolysisMineralogical Consolidation
Biological Processes
(Adapted from INAP, 2003)(Adapted from INAP, 2003)
Design Elements Addressing Issue of Sustainability
• Erosion control measures
• Revegetation plan• Growth medium layer
• Competent material• Thickness!
• Barrier layer• Geotextile• Performance
monitoring system
Performance Monitoring
P-01• Primary in situ cover
monitoring sites (x 2):• Automated• Net percolation• Suction / water content• Temperature• O2 / CO2 (manual)
P-02
• Secondary in situ cover monitoring sites (x 13) (portable soil w/c probe& O2 / CO2 gas analyzer)
• Groundwater monitoring wells• Surface runoff (automated weirs)• Meteorological monitoring
Soil Water Content Profiles Measured in 2008
0
50
100
150
200
250
300
0.00 0.10 0.20 0.30 0.40
Dep
th fr
om S
urfa
ce (
cm)
Vol. Water Content (cm3/cm3) at P-01
June 1
June 15
July 1
July 15
Aug. 1
Aug. 15
Sept 1
Barrier Layer
0
50
100
150
200
0.00 0.10 0.20 0.30 0.40
Dep
th fr
om S
urfa
ce (
cm)
Vol. Water Content (cm3/cm3) at P-02
June 1
June 15
July 1
July 15
Aug. 1
Aug. 15
Sept 1
Barrier Layer
Pit Cover Barrier Layer Saturation Levels
70
75
80
85
90
95
100
Jan
-08
Feb-
08
Mar
-08
Apr
-08
May
-08
Jun-
08
Jul-0
8
Aug
-08
Sep
-08
Oct
-08
No
v-08
Dec
-08
Dec
-08
Deg
ree
of S
atur
atio
n (%
)
P-01 Top of Barrier (n = 36%)
P-01 Middle of Barrier (n = 30%)
P-02 Top of Barrier (n = 34%)
P-02 Middle of Barrier (n = 36%)
Pit Cover Water Balance ����2006 and 2007
2006 2007
Value (mm)
Percentage of Total
Precipitation
Value (mm)
Percentage of Total
Precipitation
Precipitation 765 - 584 -
Runoff and interflow 475 62.1% 228 39.0%
Evapotranspiration 269 35.2% 332 56.8%
Net percolation 21 2.7% 16 2.7%
Change in storage 0 0 9 1.5%
Evolution of Water Treatment at Whistle
• Collection ponds surrounding former waste rock storage areas
• Water treatment plant –lime addition
• Current WTP handles pit overflow and waters collected in peripheral runoff ponds
Evolution of Water Treatment at Whistle
• Additional dam structures were constructed to increase storage capacity
Evolution of Water Treatment – Copper
0.001
0.01
0.1
1
10
2001 2002 2003 2004 2005 2006 2007 2008 2009
Cop
per
(mg
/L) -
log-
scal
e
CP3 CP3L CP2 CP1 CP5 CP6CP4 CP7 PIT C of A PWQO Background
Evolution of Water Treatment – Iron
0.01
0.1
1
10
100
1000
2001 2002 2003 2004 2005 2006 2007 2008 2009
Iron
(mg/
L) -
log-
scal
e
CP3 CP3L CP2 CP1 CP5 CP6CP4 CP7 PIT PWQO Background
Evolution of Water Treatment – Nickel
0.001
0.01
0.1
1
10
100
2001 2002 2003 2004 2005 2006 2007 2008 2009
Nic
kel (
mg/
L) -
log-
scal
e
CP3 CP3L CP2 CP1CP5 CP6 CP4 CP7PIT C of A PWQO Background
Evolution of Water Treatment – Zinc
0.0001
0.001
0.01
0.1
1
10
2001 2002 2003 2004 2005 2006 2007 2008 2009
Zin
c (m
g/L
) -lo
g-sc
ale
CP3 CP3L CP2 CP1 CP5 CP6
CP4 CP7 PIT C of A PWQO Background
Evolution of Water Treatment – pH
4
5
6
7
8
9
10
2001 2002 2003 2004 2005 2006 2007 2008 2009
pH
CP3 CP3L CP2 CP1 CP5
CP6 CP4 CP7 PIT Background
Evolution of Water Treatment – Flows
-
10,000,000
20,000,000
30,000,000
40,000,000
50,000,000
60,000,000
70,000,000
80,000,000
90,000,000
100,000,000
2001 2002 2003 2004 2005 2006 2007 2008 2009
Tota
l US
Gal
lons
Discharge Volumes
LTP Water Treated
Pit
CP1
CP2
CP3
CP4
Diverted Surface Water
• Now using 2 GE Betz products• Coagulant – METClear -
Aluminum chloride hydrate sulphate
• Metals precipitant – KLARAID - Sodium dimethyldithiocarbamate
• Lowers pH at which metals precipitate out (9.2) • Reduces lime consumption• Reduces volume of sludge
generated• Removes requirement for pH
adjustment at discharge weir• Cost savings of approximately
$186,000/yr
Evolution of Water Treatment at Whistle
Concluding Remarks
• Pit cover performing as expected …• Growth medium for a variety of local plant species• Stable landform … minimal soil erosion• H2O and O2 ingress substantially reduced since 2005
• Final landform analogous to a natural system … will aid in the sustainability of the pit cover
• Quality of site runoff and pit overflow waters improving with time
• Ultimately plan to decommission collection ponds, batch treat pit overflow water only
Recommended