SLIDE 1
Effect of Perched Water Conditions in MSW Landfills: Considerations for Landfill Operators
Timothy Townsend Department of Environmental Engineering University of Florida
ESD 17th Annual Solid Waste Technical Conference East Lansing, Michigan April 4, 2006
SLIDE 2 Motivation
- A common observation at solid waste
landfills is the possible presence of saturated waste layers in the deeper parts
- f landfills.
- The presence and cause of these
saturated layers can be interpreted differently.
- The question that we asked: “what should
- ne expect?”
SLIDE 3 LCRS Liner MSW
Consider a MSW Landfill
SLIDE 4
Install Gas Wells
SLIDE 5 LCRS Liner MSW
Consider a MSW Landfill
SLIDE 6 LCRS Liner MSW Landfill Gas Well
SLIDE 7 LCRS Liner Landfill Gas Well Water Surface
SLIDE 8 Implications of Perched Water
- Problems with gas recovery?
- Slope stability concerns?
- Leachate collection system problems?
- Future side slope seepage issues?
SLIDE 9
Landfill gas well equipped with liquid pumping system
SLIDE 10
Pump repair and maintenance
SLIDE 11 LCRS Liner Landfill Gas Well
Slope stability concerns
SLIDE 12 LCRS Liner Landfill Gas Well
Slope stability concerns
SLIDE 13 LCRS Liner Landfill Gas Well
Slope stability concerns
SLIDE 14
The implications of the perched liquids depend on their true nature within the landfill
SLIDE 15 LCRS Liner Landfill Gas Well Water Surface
SLIDE 16 LCRS Liner Landfill Gas Well Phreatic surface
SLIDE 17 LCRS Liner Landfill Gas Well
SLIDE 18 LCRS Liner Landfill Gas Well
Slope stability concerns
SLIDE 19 LCRS Liner Landfill Gas Well
Slope stability concerns
SLIDE 20 LCRS Liner Landfill Gas Well
Slope stability concerns
SLIDE 21 Let’s examine the scenario where only waste around the well is saturated Some source of water is added to the well at a rate greater that it can drain out. Possible sources:
- Gas condensate
- Perched zones of
leachate in the landfill
liquids addition
SLIDE 22
Gas Well
SLIDE 23
Soil Layer Perched Liquids
SLIDE 24
SLIDE 25 Flow1 Flow2 Flow3
Vertical Injection Wells at New River Regional Landfill
SLIDE 26
SLIDE 27 Modified Version of Richard’s Equation
( )
t S t C k z k z K r r kK r k r K
s z r r
∂ ∂ + ∂ ∂ = = + ∂ ∂ ∂ ∂ + ∂ ∂ + ∂ ∂ ∂ ∂ ψ ψ ψ ψ ψ ψ
Richard’s equation was solved using a USGS program called SUTRA
SLIDE 28 r
5 10 15 20
z
5 10 15 20
S=1 S=0.2
SLIDE 29 r
5 10 15 20
z
5 10 15 20
ψ=0 ψ=2 m ψ=4 m
SLIDE 30 r (ft)
0.0 1.0 2.0 3.0 4.0
z (ft)
10 20 30
0 ft 1 ft 2 ft 3 ft 4 ft 5 ft
Simulation Parameters K = 10-5 cm/sec Q = 17 gallons/day Duration of Moisture Addition = 10 days Head in the well ~ 8 ft
SLIDE 31 LCRS Liner Landfill Gas Well Phreatic surface
SLIDE 32
added to the landfill at a rate greater than the hydraulic conductivity, saturated conditions will result
Let’s examine the scenario where saturated conditions will develop in the landfill even if barrier layers are not present
SLIDE 33 Consider a Liquids Infiltration Pond
underneath the pond will become saturated
cover soil layers, a saturated zone will extend to the leachate collection system
SLIDE 34 LCRS Liner MSW
Consider a MSW Landfill with an Infiltration Pond
SLIDE 35 LCRS Liner MSW
Consider a MSW Landfill with an Infiltration Pond
SLIDE 36 LCRS Liner
Consider a MSW Landfill with an Infiltration Pond h d
d d h i + =
SLIDE 37 LCRS Liner MSW
Consider a MSW Landfill with an Infiltration Pond
SLIDE 38 LCRS Liner MSW
Consider a MSW Landfill with an Infiltration Pond
SLIDE 39 LCRS Liner MSW
Consider a MSW Landfill with an Infiltration Pond
Water Level
SLIDE 40 Can saturated conditions develop if the liquids are added at a rate less than the permeability of the waste?
permeability of the waste is reduced with depth
Decreasing Permeability
SLIDE 41 Col 21 vs Col 22
Density (t/m3)
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
Hydraulic Conductivity (m/sec)
10-8 10-7 10-6 10-5 10-4 10-3
At ~1400 pcy K = 8x10-5 cm/sec
SLIDE 42 Air permeability of waste at NRRL at different depths
Air Permeability, k (X10-12 m2)
<0.1 0.1-2.5 2.5-5.0 5.0-7.5 7.5-10.0 10.0-12.5 12.5-15.0 15.0-17.5 17.5-20.0 20.0-22.5 22.5-25.0 >25.0
Number of Locations
3 6 9 12 15
SLIDE 43 Air Permeability, k (X10-12 m2)
<0.1 0.1-2.5 2.5-5.0 5.0-7.5 7.5-10.0 10.0-12.5 12.5-15.0 15.0-17.5 17.5-20.0 20.0-22.5 22.5-25.0 >25.0
Number of Locations
3 6 9 12 15
Air permeability of waste at NRRL at different depths
SLIDE 44 Air Permeability, k (X10-12 m2)
<0.1 0.1-2.5 2.5-5.0 5.0-7.5 7.5-10.0 10.0-12.5 12.5-15.0 15.0-17.5 17.5-20.0 20.0-22.5 22.5-25.0 >25.0
Number of Locations
3 6 9 12 15
Air permeability of waste at NRRL at different depths
SLIDE 45 Bottom Liner Compacted MSW Leachate Collection System
27 Gpd K=10-4 cm/s K=5X10-5 cm/s
60 ft
SLIDE 46 Pressure (ft of w.c.)
2 4 6 8
Depth (ft)
10 20 30 40 50 60
SLIDE 47 Simulation Parameters Decreasing K = 10-5 cm/sec (top) to 5X10-6 cm/sec (bottom at 60 ft deep) Q = 8.5 gallons/day Duration of Moisture Addition = 10 days Head in the well ~ 5 ft
r (ft)
0.0 1.0 2.0 3.0 4.0
z (ft)
10 20 30
0 ft 1 ft 2 ft 3 ft 4 ft
SLIDE 48 Review
- The existence of standing liquids in gas
wells in landfills does not necessarily result from a phreatic liquid surface in the landfill.
- Liquids added to wells as a result of
perched layers in the landfill, gas condensate or other sources can result in relatively large depths of water in the well.
SLIDE 49 Review
- The decreasing permeability of landfilled
waste with depth should have impact.
- Saturated waste conditions may be
present, but the pressure of this water may not be accurately reflected by the depth of water that would be measured if a well was installed.
- At large liquid addition rates, saturated
conditions in deeper layers may develop.
SLIDE 50 Implications
- The presence of liquids in gas wells in
“dry” landfills should not automatically assumed to represent a phreatic surface.
- In “wet” landfills, the liquid levels in wells
may result from both situations.
- When evaluating slope stability, careful
thought must be given to the pressures that truly occur.
- Leachate collection systems need to be
designed and operated correctly.
SLIDE 51 New Experiment in Florida Bury piezometers in waste vertical well and horizontal trench
SLIDE 52 25’ Between Wells Well #1 Well #2 10’ VW Piezometer Well Injection Wells 5’ Current Bioreactor
SLIDE 53 MSW 10’ 5’ 20’ 30’ 40’ VW piezometers Data Station Injection Well #1 Cover Soil 10’ 20’ 35’ Injection Well #2
SLIDE 54 Piezometer
- Is an instrument to measure pressure
– Specifically, the Water Pressures within the Pores caused by Recirculating Leachate
Installed in Cotton bags with moist sand
SLIDE 55 Injection line Cross-Section
Vibrating Wire Peizometer Grid
SLIDE 56
SLIDE 57
SLIDE 58
SLIDE 59
SLIDE 60
SLIDE 61
SLIDE 62
SLIDE 63 Data logger for transducers installed in the summer
SLIDE 64 Piezometer T212
14.45 14.5 14.55 14.6 14.65 14.7 14.75 14.8 14.85 5 10 15 20 25 30 35 Days of December Absolute Pressure (psi) Barometer T212
SLIDE 65 Bioreactor Research in Florida
has been practiced in Florida since the 1980s
currently involved with bioreactor activities at multiple landfills
SLIDE 66
New River Regional Landfill Alachua County Southwest Landfill Polk County North Central Landfill
SLIDE 67
SLIDE 68 Instrumented Well Field
SLIDE 69
SLIDE 70
C&D Debris Issues
SLIDE 71
Crush and Load Gypsum Drywall
SLIDE 72
Install Gas Distribution System
SLIDE 73 Fine concrete 3% Ca(OH)2 1% Ca(OH)2
S a n d
Compost 10% CaCO3
Testing Plots
S a m p l i n g T u b e s Fine concrete 3% Ca(OH)2 1% Ca(OH)2
S a n d
Compost 10% CaCO3
Testing Plots
S a m p l i n g T u b e s
SLIDE 74 Jerome Meter Flux Chamber Thermometer Flow Meter N2 Gas
SLIDE 75
EWaste Impacts on Landfills
SLIDE 76
SLIDE 77
SLIDE 78
Cell Phones
SLIDE 79 Contact Info
- Tim Townsend – ttown@ufl.edu
- www.ees.ufl.edu/homepp/townsend
