Sustainable ET Landfill Caps –A Closer Look at Hydraulic … · 2016. 7. 28. · Sustainable ET...
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Sustainable ET Landfill Caps – A Closer Look at Hydraulic Equivalency
Milind V. Khire, Ph.D., P.E.Department of Civil & Environmental Engineering
Michigan State University, E. Lansing, [email protected]
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Megafills
Source: Qian et al.
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Source: Qian et al.
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Source: Benson et al. (2001)
Typical Lysimeter (ACAP)
1.5 mm LLDPEGeomembrane
(textured both sides)Percolation Pipe(25 mm PVC)
EarthenBerm
GeocompositeDrain
20 m
0.2 mEarthenBerm
Cover (thickness site specific)
Site InterimCover Soil
(thickness varies)
GeosyntheticRoot Barrier
Sump LeakTest Pipe LLDPE Cutoff
Welded to BaseGeomembrane
LLDPE CutoffWelded to BaseGeomembrane
EarthenBerm
(0.3 m)
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Lysimeters vs. Actual Final Caps –Hydraulic Differences
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Geomembrane(Zero Flux)
• Equivalency Demonstration Required • Percolation needs to be < few mm/year for an ET Cap
to receive permit
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Numerical Simulation using Vadose/W
Source: Khire and Mijares (2008)
• Unit Gradient vs. Seepage Face• Simulation of drainage layer –
Capillary Break?
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0
20
40
60
80
100
120
140
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Aver
age
Mon
thly
Pre
cipi
tatio
n (m
m)
Ave. Annual Precipitation = 731 mm/yrEstimated Annual PET = 1,076 mm/yr
PET/P = 1.47
Precipitation Data - Detroit
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Finite-Element Mesh in Vadose/W: 2-D
• Only Capillary flow considered• Flow through cracks needs to be simulated
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Simulated Percolation: Upward vs. Downward
-400
-300
-200
-100
0
100
200
0 200 400 600 800 1000 1200 1400200
250
300
350
400
450
500
Time (days)
Cum
ulat
ive
Per
cola
tion
(mm
)
KWL
X 10
KWL
X 1
Lysimeter
KVL
X 10 and KSL
X 100
Source: Khire and Mijares (2008)
(Day 699)
Downward FluxUpward Flux (ET)
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Simulated ψ Profiles: Day 699 (Downward Percolation)
1.0
2.0
3.0
4.0
5.0
6.0
-100-80-60-40-20
Matric Suction (kPa)
Ele
vatio
n (m
)
Lysimeter KVL
X 10 & KSL
X 100
KWL
=
X 1
00
X 10X 1
Day 699
SL
WL
VL
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Simulated Percolation: Upward vs. Downward
-400
-300
-200
-100
0
100
200
0 200 400 600 800 1000 1200 1400200
250
300
350
400
450
500
Time (days)
Cum
ulat
ive
Per
cola
tion
(mm
)
KWL
X 10
KWL
X 1
Lysimeter
KVL
X 10 and KSL
X 100 UpwardFlux
due toEvaporation
UpwardFlux
absent
Source: Khire and Mijares (2008)
(Day 902)
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1.0
2.0
3.0
4.0
5.0
6.0
-1200-1000-800-600-400-2000200
Pore Water Pressure (kPa)
Ele
vatio
n (m
)
Lysimeter
KWL
=
X 1
00X
10
X 1
SL
WL
VL
KVL
X 10 & KSL
X 100
Day 902
Simulated ψ Profiles: Day 902 (Upward Flux)
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Simulated Relative Percolation(Capillary Flow Only)
TVL
= 0.3 mT
SL= 1.0 m
TWL
= 3.3 mBenson and Wang (1998) MSW
-1
-0.5
0
0.5
1
1.5
2
2.5
310-6 10-5 10-4 10-3 10-2 10-1 100
Rat
io o
f Ann
ual P
erco
latio
n (P
r CA
P/Pr LY
S)
Hydraulic Conductivity of Waste Layer, KWL
(cm/s)
Upward Flux
DownwardPercolation
K VL
/KSL
:
Commonly Reported Values
10-5 /10-7(CL)
10-4 /10-6(ML)
10-3 /10-5(SM-ML)
LysimeterOverestimatesPercolation
0.8 -1.4/11.7
0.2-0.3/0.40.1/0.001
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Field-Scale Testing
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25’
2.5’
Small-Scale Lysimeter
GeomembranePea
Gravel
~ Waste ~
14 ?
SensorNest 3
Sensor Nest 2
Nest 1
6’’
1’
2’
≥ 2.5’
TVL = 1 ft
TSL = 3.5, 5 ft
Cross Section BB’
Not to Scale
Water Content and Water Potential Sensors
Gas Pressure Sensor
Liquid Level Sensor
Legend:
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Lysimeters
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Lysimeters
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Completed Test Sections
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Field Data (Preliminary)
200
220
240
260
280
300
320
340
360
Sep/
1
Oct
/1
Nov
/1
Dec
/1
Jan/
1
Feb/
1
Mar
/1
Apr/1
Soil
Wat
er S
tora
ge (m
m)
2007 to 2008
NT
NM
NB
NORTH TEST SECTIONStorage Layer
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Summary
• Percolation through lysimeters may not be representative of the percolation through an actual cap – Waste Layer Present
• Gas pressures in the landfill will also impact percolation for actual caps
• Saturated and unsaturated properties of waste and flow through cracks will influence actual percolation
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Acknowledgements
• Waste Management, Inc.• Environmental Research &
Education Foundation