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Leachate Collection Systems. Class Objectives  To discuss landfill water balance  To present liner and leachate collection system (LCS) design information.

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Presentation on theme: "Leachate Collection Systems. Class Objectives  To discuss landfill water balance  To present liner and leachate collection system (LCS) design information."— Presentation transcript:

1 Leachate Collection Systems

2 Class Objectives  To discuss landfill water balance  To present liner and leachate collection system (LCS) design information  To discuss clogging problems

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4 Liner and LCS Design  Select liner type  Leachate flow rates (25-yr storm in/hr)  Pipe spacing  Pipe flow  Pipe diameter  Design filter

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6 Waste Containment Liners Common containment regulations require different sealing systems for nonhazardous and hazardous containments. In general the lining system is a composite lining system. Waste Leachate collection Protection geotextile Geomembrane Geosynthetic Clay Liner Subsoil

7 Liner Types  Composite –Soil (clay – 60 cm, cm/sec) –Geosynthetic (1.5 mm) –Geocomposite  Double

8 Single Composite Liner

9 Double Geomembrane Liner Geomembrane or GCL

10 Double Liner with Bottom Geocomposite Composite

11 Double Composite Liner

12 Low permeability soil k d = 1 x cm/sec Subgrade t Materials in Liner system ~ Clay Liner

13 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. Geomembrane

14  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 . Geosynthetic Clay Liner (GCL)

15 Leachate Collection System

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18 Installation of a GCL barrier in the base of a MSW landfill

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23 Drain design configurations

24 Leachate Collection System with Sloped Subgrade

25 Head on Liner – Florida Regulations (Composite Liner)

26 Leachate Collection System

27 Pipe Spacing L/2  H max Slope Collection pipe q k

28 Spatial Distribution of Head (McEnroe’s Equation)

29 Slotted Collection Pipes

30 Spacing Between Pipes Using a Geonet

31 Leachate Removal System

32 Pipe flow Q in pipe = q Lb Where: q = Infiltration rate, L/T L = pipe spacing, L b = length of pipe, L

33 Pipe Diameter  Assume pipe is flowing full  Use Manning Equation  check velocity is sufficient (>2 fps)  Diameter is commercially available (not 3.2 in!)

34 Leachate Collection – Double Liner

35 Leachate Collection Pump

36 Causes of Leachate Collection System Failure  Clogging due to particulate transport/chemical precipitation  Clogging due to biological material buildup  Pipe breakage/slope change

37 Biological Clogging  Bacteria secret extra cellular polysaccharides to form gelatinous matrix or biofilm  Biofilm acts as a filter within filter, trapping particles

38 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

39 Implications of LCS Failure  Excess head on liner  Increased risk associated with potential liner failure  Side seeps  Reduced leachate output  Landfill instability

40 LCS Failure Contributors  Carbonate in drainage rock/leachate interaction  Geotextile-wrapped collection pipes  Slope change due to settling and compression of subgrade  Crushed pipe

41 LCS Failure Contributors - Cont’d  Overhandling of drainage material - production of fines  Creep/clogging of geonets  Adverse leachate pH  Change in partial pressure of CO 2

42 Clogging Prevention  Proper filter design –Use of safety factors –Proper placement  Proper selection of materials

43 Backflushing has Transitory Impact on Filter Clogging

44 Return to Home Page Last updated April 18, 2015 by Dr. Reinhart


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