CPWM Landfill Design and Operations 2 — Questions and Answers
Question 1: What is the primary purpose of a leachate collection and removal system (LCRS) in a municipal solid waste landfill?
- To prevent stormwater from entering the landfill
- To collect and remove contaminated liquid that percolates through waste (Correct answer)
- To distribute gas evenly throughout the landfill
- To monitor groundwater levels beneath the facility
Correct answer: To collect and remove contaminated liquid that percolates through waste
An LCRS collects leachate—liquid that has percolated through waste and picked up contaminants—and removes it to prevent liner breaches and groundwater contamination.
Question 2: Under RCRA Subtitle D, what minimum slope is typically required for the bottom liner of a municipal solid waste landfill to ensure proper leachate drainage?
- 1%
- 2% (Correct answer)
- 5%
- 10%
Correct answer: 2%
Subtitle D regulations require a minimum 2% bottom slope to ensure leachate drains toward collection pipes rather than pooling on the liner.
Question 3: Which type of soil is most commonly specified as a component of composite liner systems because of its low hydraulic conductivity?
- Sandy loam
- Compacted clay (Correct answer)
- Silty sand
- Gravel
Correct answer: Compacted clay
Compacted clay with hydraulic conductivity ≤1×10⁻⁷ cm/s is specified under RCRA regulations as the soil component of composite liner systems.
Question 4: What is the function of a geomembrane in a landfill liner system?
- To provide structural support for heavy equipment
- To act as a primary barrier preventing leachate migration (Correct answer)
- To promote biodegradation of organic waste
- To filter suspended solids from leachate
Correct answer: To act as a primary barrier preventing leachate migration
A geomembrane (typically HDPE) serves as a flexible, near-impermeable barrier that prevents leachate from migrating into native soil and groundwater.
Question 5: Daily cover is required at active landfills primarily to:
- Increase the compaction density of waste
- Control odors, vectors, and fire, and reduce litter (Correct answer)
- Accelerate methane gas generation
- Improve leachate quality before collection
Correct answer: Control odors, vectors, and fire, and reduce litter
Daily cover—typically 6 inches of soil or approved alternative—controls odors, vectors (rodents, birds), blowing litter, and fire hazards.
Question 6: A landfill operator notices that the leachate collection pipes are draining more slowly than usual. What is the most likely cause?
- Increased rainfall causing diluted leachate
- Biological clogging or sedimentation in the drainage layer (Correct answer)
- Elevated landfill gas pressure suppressing flow
- Geomembrane expansion reducing pipe diameter
Correct answer: Biological clogging or sedimentation in the drainage layer
Biological clogging (biofouling) and sedimentation of fine particles in the granular drainage layer are the most common causes of reduced LCRS flow rates.
Question 7: Which landfill operational practice helps maximize the airspace utilization and structural stability of the waste mass?
- Spreading waste in thin lifts without compaction
- Compacting waste in 2-foot lifts using a landfill compactor (Correct answer)
- Placing waste in large uncontrolled mounds
- Mixing waste randomly to improve settlement
Correct answer: Compacting waste in 2-foot lifts using a landfill compactor
Compacting waste in 2-foot (approximately 0.6 m) lifts with a landfill compactor maximizes density, conserves airspace, and improves slope stability.
CPWM Landfill Design and Operations 2
What is the primary purpose of a leachate collection and removal system (LCRS) in a municipal solid waste landfill?