Landfill Gas Case Study: Lessons Learned and Design Considerations

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Landfill Gas Case Study Lessons Learned and
Design Considerations

• Lori A. Winters and Sean C. Paulsen
• MWIA/ESD 2009 Solid Waste Conference

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Discussion Outline

• Chronology of Events
• Response Activities
• Future Plans and Steps
• Lessons Learned

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In the Beginning

• Groundwater Monitoring Data and Results
• Dissolved iron and manganese
• Other inorganic constituents
• Landfill Gas Monitoring Results
• Methane levels increase along western boundary
• Unable to tune field to control LFG

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Redox Sensitive Parameters

• Redox sensitive parameters generally unreliable
  for monitoring
• Field sampling variability
• Well construction materials
• Landfill construction

Dissolved Iron
Dissolved Manganese
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Inorganic Indicators

• Conservative parameters more reliable for
  landfill impacts
• Not influenced by oxidation processes
• PROBLEM only indicate leachate impact

Chloride
Dissolved Potassium
Nitrogen-Ammonia
Dissolved Sodium
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10,000 Foot View

• Iron and manganese initially increased along
  north
• Oldest portion of the landfill in northwest
  corner
• Focus initial investigation on northwest

Zone of initial increases2004-2005
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Landfill Gas Contours
Percent Methane in Landfill Gas Extraction Wells
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Landfill Gas Contours
Percent Oxygen in Landfill Gas Extraction Wells
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Results of Contouring

• Northwest corner has relatively low gas
  production
• Oxygen levels in northwest corner are relatively
  high
• Pulling harder will create NSPS or plant problem
• Lack of gas wells in central portion of landfill
• Other potential sources for LFG?

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10,000 Foot View (Part 2)

• Iron and manganese begin to increase along south
  landfill boundary
• No migration issues along south unable to
  control west
• Change the focus of the investigation
• Relationship between the two areas?

Zone of initial increases2004-2005
Zone of later increaseslate 2007
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Redox Sensitive Parameters

• Redox sensitive parameters generally unreliable
  for monitoring
• No VOCs or gas parameters
• Added dissolved methane analyses

Dissolved Iron
Dissolved Manganese
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Groundwater Contour

• Channel Fill Aquifer stretches between two zones
  where methane detected
• Geology is an old stream channel
• Need to determine potential as a migration pathway

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Hydrogeologic Investigation
Cross-Section Location Map
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Hydrogeologic Investigation

• Two aquifer zones Channel Fill and Outwash
  Aquifer
• Channel Fill Aquifer also extends between west
  and south boundaries
• Clay lined cells in north and central portion of
  landfill

Unsaturated zone
East-West Cross-Section
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Hydrogeologic Investigation

• Cells 1 and P are double-composite lined cell
• Cells N and O recompacted clay liner
• Is the construction of composite cells over clay
  lined cells adding to the problem?

North-South Cross-section
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Piggyback Liner
Area with CompactedClay Liner
Area of PiggybackOverliner
Gas Well Location Map with Piggyback Liner Areas
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Problems

• Older, clay lined areas are overlain by composite
  lined cells gas collection system essentially
  abandoned during construction
• Landfill gas in older portion of landfill is
  trapped beneath lined areas
• Rules dont allow penetration of piggyback liner
• Due to pressure build-up, landfill gas in older
  cells moving through clay liner into subsurface

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Response Actions

• Source area appears to be central portion of
  landfill
• Met with MDEQ to discuss options
• Complete pilot boring using hollow stem auger and
  split spoon samples
• Locate depth of piggyback liner
• Monitor methane levels
• Grab samples to determine moisture content of
  waste material

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Response Actions (cont.)

• Install first round of piggyback wells
• Single well only bentonite seal at and above
  piggyback liner
• Install dual extraction wells
• One above and one below liner
• Install out-of-waste collectors on west side

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Completion of Pilot Borings

• Piggyback liner settled an average of 10
• Waste material located above piggyback liner very
  dry
• Waste material below piggyback liner variable
  moisture
• Incr. moisture content incr. gas production

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Dual Gas Well Detail

• Both wells constructed of Schedule 80 PVC
• Ten foot thick bentonite seal placed at piggyback
  liner 5 above and below
• 1 to 3 stone backfill placed around slotted
  portion
• Minimum 2 between slots and seal

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Installation of Dual Gas Wells

• Six dual wells total of ten piggyback wells
• Two wells installed in each 36 diameter boring
• 6 well is shallow installed above liner
• 8 well is deeper below liner

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Install Out-of-Waste Collectors

• Continued control issues with subsurface landfill
  gas levels along western boundary
• Methane concentrations further indicate source is
  not northwest corner, but newer waste
• Installed 3 out of waste collectors along western
  boundary to control methane
• Collectors have been successfully controlling gas
  for approx. 2.5 months
• Condensate sump critical and very active

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Out-of-Waste Collectors

• Three wells along west perimeter to intersect
  Channel Fill
• 200 foot spacing
• 3 PVC well with 2 well head
• Condensate sump is the key to system operation

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Next Steps

• Continue Gas Extraction from New Gas Wells
• Since new wells, gas production increased from
  1400 to 1900 scfm
• Half of the difference from piggyback wells
• May need additional piggyback wells?
• Continue Out-of-Waste Collection
• Maintain gas levels along landfill boundary
• Continue Monitoring Sensitive Parameters
• Dissolved iron and manganese
• Dissolved methane

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Landfill Gas Contours
Percent Methane in Landfill Gas Extraction Wells
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Chemistry Changes

• Since install of new wells, diss. iron levels
  have stabilized or decreased
• Diss. methane has stabilized or decreased
• Diss. methane typically responds first, and
  inorganics follow

Dissolved Iron
Dissolved Methane
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Lessons Learned

• Normal leachate indicators may not identify gas
  issues
• Redox sensitive parameters function well as
  landfill gas indicators
• Source isnt always obvious think big picture
• If gas is potential source, include dissolved
  methane testing VOCs dont always show up
• No quick fix issues take time to resolve

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Lessons Learned (cont.)

• Plan for gas extraction before installing
  piggyback liners
• Passive vs. active
• Tweak dual well design
• Re-evaluate function of piggyback liners
• Some states dont require piggyback liners
• The gas is where the moisture is
• Condensate sump critical to out-of- waste
  collectors

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• Questions/Comments