Leachate Management Leachate Control and Collection

Leachate Management Leachate Control and Collection

Leachate Collection Sanitary landfills have leachate collection and removal system above liner At un-lined landfills and dump sites Perimeter Ditch - can be used to drain leachate and carry it to treatment system Subsurface Perimeter Gravity Drain (aka Toe Drain, French Drain) - can be built around waste

Leachate Control Control of leachate migration starts by properly siting, designing, constructing, and operating the solid waste disposal site Bottom Liner Drainage slopes Collection and removal system

Bottom Liner System Design Low permeability (clay) liner Natural (in place) Re-compacted clay Geosynthetics Single geosynthetic layer Double synthetic liner (with or without leak detection) Composite liner Combination of Clay and Geosynthetics With or without leak detection

Leachate Collection Bottom Liner

Example Liner System Double Liner with Composite

Typical Layout of Leachate Collection System (top view)

Side View of Leachate Drainage Slopes

Design Leachate Flow Model conceptual designs to assess leachate generation and flow Use generation and flow calculations to design leachate management components: Drainage media Pipes and spacing Collection sump Leachate pumps Discharge gravity and force mains Storage tanks Tanker trucks Treatment option

Leachate Collection Systems Purpose To efficiently convey leachate off of liner and minimize pressure head over the liner (30 cm max. per Subtitle D US regulation) 11

Leachate Collection Systems Proper precautions when designing the leachate management system and maintaining the extraction system, whether manual or automatic, are essential to avoid clogging of the system. Blockage of the leachate system is caused by: Sedimentation Biological growth Pipe breakage or deterioration. 12

System Components Drainage media (high permeability) Sand or Gravel Geonet or geocomposite drainage net Other: tire chips, crushed glass Protective cover: Material between drainage layer and waste Granular media (sand or gravel) Geotextile Other: tire chips Pipe (HDPE)

Leachate Collection Collection Pipe Above Liner

Leachate Surface Discharges Obvious Visual Impact 15 15

16 Leachate Collection Layer at Battle Creek Landfill Cell 8

Drainage Media: Design Parameters Hydraulic Conductivity, k (coefficient of Permeability) Sands: 10-4 cm/s k 10-2 cm/s Gravels: 10-2 cm/s k 100 cm/s Geonets: 1 to 34 cm/s Chipped Tires 10-2 cm/s k 100 cm/s Must factor in compressibility under loading Darcy s law q = kia (Laminar flow) Q = rate of flow i = hydraulic gradient a = gross cross sectional area through which flow occurs Flow Velocity v = ki Velocity through pores, v = ki/n Transmissivity (T) = k x thickness of layer

Drainage Media: Design Parameters Slope (s) Liner placed at minimum 1 to 2% slope for leachate collection Maximum allowable pressure head (h) of leachate per Subtitle D (US regulation) 30 cm (12-inches) Distance (L) between collection pipes dependent on: Maximum pressure head Pipe size Slope Leachate flow

Design Steps Establish bottom liner geometry Estimate initial collection system geometry Estimate infiltration to drainage layer (HELP Model) Evaluate head over liner Revise bottom liner or collection system geometry as needed (pipe spacing revisions) Determine required pipe size and strength Size sumps Size pumps Size gravity/force mains Select material specifications

Pipe Design Pipe sizing Leachate flow rate Area flowing to pipe Pipe slope Use Manning s equation for design Pipe Strength Wall crushing Wall buckling Ring deflection Loading based on material over pipe and vehicle traffic (transfer trailer/compactor)

21 Leachate Collection Layer and Piping at Arthurstown Landfill, Ireland

Pumps and Sumps Area Purpose: Provide collection point for pumping leachate Location: Function of design configuration, low point Sizing based on: Leachate flow rate Desired pump cycle time Type: Submersible May have redundant pump system or back-up pumps available Sizing ancillary components (electrical) for largest pump anticipated Control systems

Typical Leachate Collection System 1 FT ALLOWABLE LEACHATE HEAD LEVEL (EXAGGERATED FOR DEMONSTRATION) LEACHATE COLLECTION PIPE LEACHATE RISER PIPE PUMP TOP OF LINER SUMP

Leachate pumps in LFG Wells Used to pump leachate out of the LFG wells Types Electric submersible (centrifugal) Air-powered automatic Piston

Summary Modeling can be a useful tool to estimate leachate generation on a site specific basis Components of leachate collection system require careful design to ensure proper performance