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Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Appropriate Concepts andCriteria For the Design of
Cover Systemsby
G. Ward Wilson
Appropriate Concepts andCriteria For the Design of
Cover Systemsby
G. Ward Wilson
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Key Components & Criteria● Continuum across soil - atmosphere
boundary● Infiltration - mass transfer● Evaporation - heat & mass transfer● Surface properties● Vegetation, Runoff & Erosion● Design Issues● Material Science - Waste as a
Resource
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
The Soil-Atmosphere ContinuumThe Soil-Atmosphere ContinuumThe Soil-Atmosphere Continuum
Unsaturated Soil
PrecipitationPrecipitation
EvapotranspirationEvapotranspiration∆∆
Saturated Soil
Capillary Fringe
Ground SurfaceDry Soil
Two Phase Soil
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Atmospheric Forcing EventsAtmospheric Forcing EventsAtmospheric Forcing Events
EvaporationTranspirationExfiltration
Infiltration RainfallSnowmelt
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Infiltration and RunoffInfiltration and Runoff and Runoff
Time (sec)
Infil
trat
ion
Cap
acity
(m
/sec
)
K s
Runoff
Infiltration dueto Ponding Rainfall Intensity
Quantity of Infiltration
δh = Cw δ (Kw δh)δt δy δy
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Conventional Methods Availablefor theEvaluation of Evaporation
●Thornthwaite Method●Penman Method●Priestley - Taylor Method●Complimentary Relationship
These methods are based onclimatic conditions only
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
AE
/PE
(%)
100
0
SandSlow Drying
Clay
Sand Fast Drying
MoistureAvailabilityField
CapacityPermanentWilt Point
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
AE / PEAE / PE vs vs. Suction. Suction
101011 101033 101055
Suction (kPa)Suction (kPa)101022 101044 101066
00
0.50.5
11
1.51.5
22
AE
/ P
EA
E /
PE
Beaver Creek SandCustom SiltRegina Clay
Beaver Creek SandCustom SiltRegina Clay
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Relative Humidity & Suction
0
25
50
100 102 104 106
Suction (kPa)
R.H
. (%
) 75
100
R H e
WRT
v
. .=Ψ
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Stem = 500 kPaRoot = 200 kPa
Soil = ? kPa
Leaf =1500 kPaEvaporation
Cohesion(in xylem)
WaterUptake(fromthesoil)
Air
Air
Air
H2OH2O
Atmosphere = 100,000 kPa(50% r.h. at 22oC)
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Soil Atmosphere Model
●Climatic Conditions +
●Surface Characteristics
Soil PropertiesGroundwater Conditions
Vegetation
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
An Oxygen and Water BarrierAn Oxygen and Water BarrierAn Oxygen and Water Barrier
PrecipitationPrecipitation
RunoffRunoff
EvapotranspirationEvapotranspiration
Reactive Waste
Soil Reinforced Water Cover
..
MinimizeNet Infiltration
O2
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Store/ReleaseStore/Release
PrecipitationPrecipitation
∆ ∆
EvapotranspirationEvapotranspiration
Net InfiltrationNet Infiltration
StorageStorageθr 100%
Effective Saturation
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Soil-Water Characteristic CurveSoil-Water Characteristic Curve
VolumetricWater Content High
Storage
Low Storage
Controls: i) Gradationii) Silt and Clay Contentiii) Density and Structure
Suction
High AEV
Low AEV
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Kidston - IntroductionKidston - Introduction
Reclamation at the Kidstonmine site presents a specialcase since the tailings surfaceand final cover system aresubject to extreme wet and dryconditions.
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Precipitation and Potential Evaporation
1000
800
600
400
200
0July‘90
Sept.‘90
Nov.‘90
Jan.‘91
Mar.‘91
May‘91
Date
Flu
x (m
m/m
onth
)
Cumulative P.E. = 1907 mmCumulative Precipitation = 1349 mm
Cumulative P.E. = 1907 mmCumulative Precipitation = 1349 mm
PE > ppt.PE > ppt.PE > ppt.
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Zero Flux Cover DesignAlternatives Considered for Kidston
Vegetation
1.5 mnon-compacted
oxide cap0.5 m compacted
oxide cap
waste rock
● Storage SystemVegetation
2.5 mnon-compacted
oxide cap
waste rock
● Barrier/Stora ge System
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBCSuction (kPa)
Vol
umet
ricW
ater
Con
tent
(de
c.)
SWCC
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.1 1 1e1 1e2 1e3 1e4 1e5 1e6
Non-compactedOxideCap
CompactedOxideCap
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Vol. w/c versus Depth
Volumetric Water Content
Dep
th (
m)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.00 0.10 0.20 0.30 0.40
Day 100Day 200Day 300
5 mwaste rock
2 m oxide cap
0.5 m compactedoxide cap
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Net Infiltrative Flux
Simulation NumberNet
Flu
x F
rom
Bas
e of
Cov
eras
a P
erce
ntag
e of
Tot
al R
ainf
all
yr. 2
-1%
0%
1%
2%
3%
4%
5%
yr. 1
yr. 1
yr. 2
Barrier/StorageSystem Storage System
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Appropriate Concepts for TheDesign of Soil Cover SystemsAppropriate Concepts for TheAppropriate Concepts for TheDesign of Soil Cover SystemsDesign of Soil Cover Systems
EcosystemEcosystem - Biosphere- Biosphere
Living Soil SystemLiving Soil System - Organic/mineral media- Organic/mineral media(A and B horizons)(A and B horizons) - Buffer/Protector- Buffer/Protector
Barrier SystemBarrier System - Engineered Properties- Engineered Properties(C horizon)(C horizon) - Permeability/flow- Permeability/flow
- Change characteristic- Change characteristic water storage and volume water storage and volume
Isolated SystemIsolated System - Mine Waste- Mine Waste
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Material ScienceMaterial ScienceMaterial Material CharacteristicsCharacteristics
TypeType PermeabilityPermeability Storage Storage StabilityStability CompressibilityCompressibility
ClayClay very lowvery low very lowvery low very low very low very highvery high
SiltSilt moderatemoderate highhigh very low very low moderatemoderate
SandSand highhigh lowlow high high lowlow
GravelGravel very highvery high very lowvery low very high very high very lowvery low
Well GradedWell Graded moderatemoderate low to low to highhigh lowlow
MaterialMaterial highhigh
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Equity Silver Case StudyEquity Silver Case StudyEquity Silver Till is a Proven Performer
1.) Dense Well Graded Material
2.) Low Hydraulic Conductivit y and a High AEV
3.) High Shear Strength
4.) Resistant to erosion
5.) Good Workability
6.) Cost Effective
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
0
10
20
30
40
50
60
70
80
90
100
0.010.1110100
Per
cent
Fin
er T
han
Grain Size - (mm)
KidstonWaste Rock
Alaskan Till
KidstonOxide
Equity Till
Kidd CreekTailings
Grain Size DistributionGrain Size Distribution
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Vol
umet
ric W
ater
Con
tent
(%
)V
olum
etric
Wat
er C
onte
nt (
%)
Suction (kPa)Suction (kPa)
0.000.00
0.080.08
0.160.16
0.240.24
0.320.32
0.400.40
0.480.48
101000 101022 101044 101066
Kidd Creek Tailings
Equity Till
Kidston Waste Rock
Soil-Water Characteristic CurvesSoil-Water Characteristic Curves
Kidston Oxide
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Zone ofNegativeWaterPressure
Precipitation
RunoffEvapotranspiration
CoverWaterTable
Tailings
Zone ofPositiveWaterPressure
Drainage
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Water contentWater contentw%w%
Net normal stressNet normal stress((σσmeanmean - - u uaa) )
Matric suction Matric suction ((uuaa - - uuww))
Constitutive SurfaceConstitutive Surface
Mining and the Environment UBC Mining and the EnvironmentMining and the Environment UBCUBC
Summary and ConclusionsSummary and Conclusions
● Soil Atmosphere Approach For Design● Well Graded Materials are Best● Using Waste as a Resource
– cost– construction equipment– construction materials
● Benefits
● Soil Atmosphere Approach For Design● Well Graded Materials are Best● Using Waste as a Resource
– cost– construction equipment– construction materials
● Benefits
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