Transcript Are Florida Landfill liner Systems Clogging and How Would

Leachate Collection Systems
Class Objectives
To discuss landfill water balance
To present liner and leachate collection
system (LCS) design information
To discuss clogging problems
Liner and LCS Design
Select liner type
Leachate flow rates (25-yr storm - 0.36
in/hr)
Pipe spacing
Pipe flow
Pipe diameter
Design filter
Waste Containment Liners
Waste
Leachate collection
Protection geotextile
Geomembrane
Geosynthetic Clay Liner
Subsoil
Common containment regulations require different
sealing systems for nonhazardous and hazardous
containments. In general the lining system is a
composite lining system.
Liner Types
Composite
– Soil (clay – 60 cm, 10-7cm/sec)
– Geosynthetic (1.5 mm)
– Geocomposite
Double
Single Composite Liner
Double Geomembrane Liner
Geomembrane or GCL
Double Liner with Bottom
Geocomposite
Composite
Double Composite Liner
Materials in Liner system ~ Clay
Liner
Low permeability soil
kd = 1 x 10-7 cm/sec
t
Subgrade
Geomembrane
A planar, relatively impermeable, polymeric
(synthetic) sheet with a minimum thickness of 1.0
mm. In landfill applications they are most
commonly of HDPE with a thickness of > 1.0 mm.
The surface can be smooth, profiled or
textured and can be of importance for the shear
behaviour.
Geosynthetic Clay Liner (GCL)




An assembled structure of geosynthetic materials and
low hydraulic conductivity earth materials (usually
bentonite). The clay layer is encapsulated between
geosynthetics (cover and carrier geotextile) or
bonded to a geosynthetic.
Shear force transferring GCLs are needle-punched
or stitchbonded.
Leachate Collection System
Installation of a GCL barrier in
the base of a MSW landfill
Drain design configurations
Leachate Collection System with Sloped
Subgrade
Head on Liner – Florida
Regulations (Composite Liner)
Table 1. Minimum Thickness of Lower Component of Composite Liner (in ft) as a
Function of Maximum Design Head.
Max. Design Head, in
Maximum Hydraulic Conductivity (cm/sec)
1 x 10
5 x 10-8
1 x 10-8
2
1
1
2.5
1.5
1
3
2
1
-7
1
6
12
Leachate Collection System
Pipe Spacing
q
k
Slope
Hmax

L/2
Collection pipe
Spatial Distribution of Head
(McEnroe’s Equation)
H max
Where:
Hmax =
L
=

=
q
=
k
=
1


2
2
L  q  k tan 
k tan  2
q 
  
1
tan





2k
q
q 
k 


maximum leachate head, L
distance between leachate collection pipes, L
angle of liner slope, dimensionless
leachate impingement rate, LT-1
hydraulic conductivity of the leachate
collection layer material, LT-1
Slotted Collection Pipes
Spacing Between Pipes Using
a Geonet
 reqd =
reqd
L
hmax
q

=
=
=
=
=
2
4h max
qL
+ 2Lsin
transmissivity of geonet, L2T-1
distance between collection pipes, L
maximum head on liner, L
infiltration from a 25 year 24 hour storm, LT-1
slope of drainage system, degrees
Leachate Removal System
Waste
Sand Drainage and
Protective Layer
Geotextile
Geomembrane Liner
Clay Liner
Coarse
Drainage
Material
Leachate
Collection
Pipe
Pipe flow
Qin pipe = q Lb
Where:
q = Infiltration rate, L/T
L = pipe spacing, L
b = length of pipe, L
Pipe Diameter
Assume pipe is flowing full
Use Manning Equation
check velocity is sufficient (>2 fps)
Diameter is commercially available (not
3.2 in!)
Leachate Collection – Double
Liner
Leachate Collection Pump
Causes of Leachate Collection
System Failure
Clogging due to particulate
transport/chemical precipitation
Clogging due to biological material
buildup
Pipe breakage/slope change
Biological Clogging
Bacteria secret extra cellular
polysaccharides to form gelatinous
matrix or biofilm
Biofilm acts as a filter within filter,
trapping particles
Chemical Precipitation
Metals are mobilized in leachate
Carbonates and sulfides present in
anaerobic environment lead to metal
precipitation
Little silts or other fines
Primary threat during acidic phases
Opening size critical factor
Implications of LCS Failure
Excess head on liner
Increased risk associated with potential
liner failure
Side seeps
Reduced leachate output
Landfill instability
LCS Failure Contributors
Carbonate in drainage rock/leachate
interaction
Geotextile-wrapped collection pipes
Slope change due to settling and
compression of subgrade
Crushed pipe
LCS Failure Contributors Cont’d
Overhandling of drainage material production of fines
Creep/clogging of geonets
Adverse leachate pH
Change in partial pressure of CO2
Clogging Prevention
Proper filter design
– Use of safety factors
– Proper placement
Proper selection of materials
Backflushing has Transitory
Impact on Filter Clogging
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Last updated July 17, 2015 by Dr. Reinhart