SWANA Landfill Gas Management 2 — Questions and Answers
Question 1: Under EPA surface emissions monitoring (SEM) requirements, what surface methane concentration above background triggers corrective action?
- 100 ppm
- 200 ppm
- 500 ppm (Correct answer)
- 1,000 ppm
Correct answer: 500 ppm
Under 40 CFR 60.755, a surface methane concentration of 500 ppm above background measured during SEM requires corrective action to identify and repair the source of emissions.
Question 2: What distinguishes a passive LFG collection system from an active system?
- Passive systems use blowers to draw gas
- Passive systems rely on chemical neutralization of methane
- Passive systems rely on natural pressure differentials using vents or barriers without mechanical assistance (Correct answer)
- Passive systems burn gas at each individual wellhead
Correct answer: Passive systems rely on natural pressure differentials using vents or barriers without mechanical assistance
Passive systems use the natural positive pressure generated by decomposing waste to vent gas through perforated pipes or gravel trenches, without mechanical blowers or vacuum equipment.
Question 3: What is the typical combustion temperature maintained inside an enclosed ground flare to achieve high LFG destruction efficiency?
- 300–500°F
- 600–800°F
- 2,500–3,000°F
- 1,400–1,800°F (Correct answer)
Correct answer: 1,400–1,800°F
Enclosed flares are designed to maintain combustion temperatures of approximately 1,400–1,800°F (760–982°C), achieving the 98% NMOC destruction efficiency required by EPA regulations.
Question 4: What does RNG stand for in the context of advanced LFG utilization projects?
- Refined Non-fossil Gas
- Renewable Natural Gas (Correct answer)
- Regulated Nitrogen Gas
- Recovered Natural Gas
Correct answer: Renewable Natural Gas
RNG (Renewable Natural Gas) is LFG that has been processed to pipeline-quality natural gas specifications (>95% methane) and injected into natural gas distribution systems or used as vehicle fuel.
Question 5: What pipe material is most commonly used in the construction of vertical LFG extraction wells?
- Copper tubing
- Cast iron pipe
- High-density polyethylene (HDPE) pipe (Correct answer)
- Schedule 40 PVC pressure pipe
Correct answer: High-density polyethylene (HDPE) pipe
HDPE pipe is preferred for LFG extraction wells because it is resistant to corrosion from landfill leachate, flexible enough to accommodate settlement, and durable under the acidic landfill environment.
Question 6: Which instrument is most commonly used to directly measure gas flow rate at LFG wellheads or in collection headers?
- Thermocouple probe
- pH electrode
- Pitot tube manometer
- Orifice plate or thermal mass flowmeter (Correct answer)
Correct answer: Orifice plate or thermal mass flowmeter
Orifice plates and thermal mass flowmeters are standard instruments for measuring LFG flow rates; thermal mass meters are especially accurate for low-flow conditions common in individual extraction wells.
Question 7: EPA's NSPS for MSW landfills (40 CFR Part 60, Subpart XXX) requires GCCS to reduce NMOC emissions to what minimum destruction efficiency?
- 75%
- 85%
- 90%
- 98% (Correct answer)
Correct answer: 98%
EPA requires GCCS at regulated landfills to achieve 98% NMOC destruction efficiency, or reduce NMOC concentration to 20 ppmv or less at the control device outlet.
SWANA Landfill Gas Management 2
Under EPA surface emissions monitoring (SEM) requirements, what surface methane concentration above background triggers corrective action?