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Leachate Collection Systems

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					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)
                                   -7
                              1 x 10               5 x 10-8                1 x 10-8
         1                       2                     1                      1
         6                      2.5                   1.5                     1
         12                      3                     2                      1
Leachate Collection System
Pipe Spacing
         q



k            Hmax
 Slope
                    Collection pipe
         
    L/2
Spatial Distribution of Head
(McEnroe’s Equation)
                                                         1
            L  q   k tan 2      k tan     2      q
                                                tan    
                                                           2
    H m ax                   1           
            2  k  q                 q              k 
                                                         
Where:
Hmax =     maximum leachate head, L
L      =   distance between leachate collection pipes, L
      =   angle of liner slope, dimensionless
q      =   leachate impingement rate, LT-1
k      =   hydraulic conductivity of the leachate
           collection layer material, LT-1
Slotted Collection Pipes
Spacing Between Pipes Using
a Geonet
                              2
                          qL
   reqd =
              4h max      + 2Lsin
reqd   =    transmissivity of geonet, L2T-1
L       =    distance between collection pipes, L
hmax    =    maximum head on liner, L
q       =    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

                                                        Leachate
              Clay Liner   Coarse
                                                        Collection
                           Drainage
                                                        Pipe
                           Material
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 September 8, 2011 by Dr. Reinhart

				
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