Whistle Mine: Design, Construction and Performance Monitoring … · 2017-06-27 · Whistle Mine:...

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

Site: ~60 km NW of Sudbury

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

• Extensive dam upgrade program was undertaken –engineering design and construction

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: Erosion Modeling of First Design

Landform Design: Output from Model (after 100 yrs)

Significant Gully / Rill Development and

Interill Erosion

Landform Design: Second and Final Design

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

Construction of the Pit Cover

• Started May 2004

Construction of the Pit Cover

• Completed November 2005

Pit Cover – 2009

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%

Soil Temperature Contours from 2008

Rock Armoring

Barrier Layer

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

• Former waste rock dump areas washed

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

Concluding Remarks

• Tom Peters Memorial Reclamation Award (CLRA)