Steep Slope Landfill Closure

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Steep Slope Landfill Closure

• Presented by
• Mark A. Swyka, P.E.
• Cornerstone Environmental Group, LLC
• May 2007

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Definition of a Steep Slope

• Steep is relative
• Different systems have varied tolerance to slopes

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Definition of a Steep Slope

• Challenge to traverse perpendicular to slope
  approx. 10H1V
• Challenge to traverse parallel to slope approx.
  4H1V
• Challenge to maintain approx. 3H1V
• Part 360-2.13(q) 3H1V max slope
• Difficult to work with tracked equipment
  approx. 2H1V

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Existing 1.5H1V Slope
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Existing 1.25H1V Slope
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Existing Unstable Slope Steeper Than 1H1V
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6 NYCRR Part 360-2.15(l)

• Landfills may be closed with slopes exceeding 33
  percent providing
• No Department Approved Closure Plan
• Slopes exceeded 33 percent before 12-31-88
• Stability Analysis Performed
• Final grades do not exceed 50 percent for more
  than 20 feet vertical rise
• Run-off diversion terraces must be constructed at
  vertical intervals not exceeding 20 feet

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2H1V Slopes w/ Drainage Terrace
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Design Requirements

• Under cap landfill gas venting
• Barrier layer Textured Geomembrane
• Barrier Protection Drainage Layer
• Topsoil
• Turf Reinforcement Mat (TRM)
• Vegetation

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Causes of Slope Failure

• Moisture
• Surfacewater
• Head build-up on Geomembrane
• Assumption
• Material Strengths
• Material Permeabilities

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Needs of Steep Slopes

• Site Specific Assessment
• Material Specific Testing
• Erosion Control
• Short-term TRM
• Long-term Vegetation
• Stormwater Management
• On the ground surface
• Below the ground surface
• Accessibility for Maintenance

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TYPICAL FINAL COVERWITH INTERNAL DRAINAGE PIPES
TOPSOIL
PROTECTIVE SOIL
FML
DRAINAGE PIPE
1
DRAINAGE LAYER
3 (MAX)
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TYPICAL FINAL COVERWITH GEOCOMPOSITE DRAIN
TOPSOIL
PROTECTIVE SOIL
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
FML
1
GEOCOMPOSITE DRAIN
3 (MAX)
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Landfill Z New York
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Rainfall History
RAINFALL (INCHES)
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Landfill Z New York
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Landfill X New Jersey
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Landfill X New Jersey
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Landfill X New Jersey
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Rainfall History
RAINFALL (INCHES)
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Shear Strength Requirements
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Interface Friction

• Textured Geomembrane to Soil
• Reliable to about 34 degrees
• Range can extend to more than 40 degrees
• Textured Geomembrane to Geotextile
• Reliable to about 22 degrees
• Range can be higher, but highly variable
• Product specific testing is mandatory

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STEEP SLOPE COVER WITH TENSILE ELEMENT
EMBEDMENT LENGTH
TOPSOIL
TENSILE ELEMENT
FML
DRAINAGE LAYER
1
2
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STEEP SLOPE FINAL COVERWITH INTERNAL DRAINAGE
PIPES
TOPSOIL
BARRIER PROTECTION LAYER
FML
DRAINAGE PIPE
DRAINAGE LAYER
1
2
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SIDESLOPE DIVERSION CHANNEL
DRAINAGE CHANNEL
2
1
TOPSOIL
DRAINAGE LAYER
FML
1
3
BARRIER PROTECTION LAYER
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SIDESLOPE HALF-PIPE CHANNEL
TOPSOIL
HALF-PIPE CHANNEL
BARRIER PROTECTION LAYER
1.5
1.0
DRAINAGE LAYER
FML
1
2
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The Sagamore

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Landfill Site
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Croton Watershed

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• Second level
• Third level
• Fourth level
• Fifth level

Approximate Landfill Boundary
West Branch Reservoir
Shaft 10 - NYC Delaware Aqueduct
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Town of Carmel Landfill

• Inactive Former MSW Landfill
• Footprint
• 8 Acres
• Waste Inventory
• Approximately 500,000CY
• Existing Slopes
• As Steep As 1H1V
• Inadequate Footprint to Contain Waste

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Summary

• Landfills can be closed with final slopes as
  steep as 2H1V using available materials
• Site specific and material specific testing is
  mandatory
• Erosion control is essential
• Moisture control is essential

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THANK YOU