Landfill Gas Management Flashcards

What is the lower explosive limit (LEL) of methane in air, above which methane-air mixtures become potentially explosive?

Answer: 5% by volume

Methane is flammable and potentially explosive when its concentration in air falls between 5% (LEL) and 15% (UEL) by volume, making LFG migration into enclosed structures a serious safety hazard.

LFG-to-energy projects that generate electricity at the landfill most commonly use which prime mover technology?

Answer: Internal combustion engines or combustion turbines fueled by LFG

Reciprocating internal combustion engines and combustion turbines are the most widely used technologies for direct LFG-to-electricity generation due to their efficiency, scalability, and cost-effectiveness at typical landfill gas flow rates.

What parameter is typically adjusted at individual LFG wellheads to balance gas collection evenly across a landfill wellfield?

Answer: Vacuum (negative pressure) applied to each well

Operators throttle the valve at each wellhead to adjust the applied vacuum, balancing gas yield across the wellfield and preventing excessive air intrusion from high-vacuum wells in dry or shallow waste areas.

What is the primary purpose of a landfill wellfield monitoring program?

Answer: Assess gas collection system efficiency and overall wellfield performance

Wellfield monitoring tracks gas flow rates, pressures, temperatures, and gas composition at individual wells and headers to evaluate collection efficiency, detect system problems, and maintain regulatory compliance.

Which EPA voluntary program assists landfill owners and operators in developing LFG energy projects by providing technical and financial guidance?

Answer: Landfill Methane Outreach Program (LMOP)

EPA's Landfill Methane Outreach Program (LMOP) is a voluntary assistance program that helps landfills convert LFG into a productive energy resource by connecting stakeholders and providing technical and market development support.

Off-site LFG migration from a landfill into adjacent buildings or structures poses what primary safety hazard?

Answer: Methane accumulation creating an explosion and fire risk in enclosed spaces

Methane migrating into basements, utility vaults, or buildings can accumulate to explosive concentrations (5–15% LEL-to-UEL range) in the absence of adequate ventilation, posing a serious explosion and fire risk.

During LFG wellfield monitoring, elevated nitrogen or oxygen concentrations measured in extracted gas typically indicate what condition?

Answer: Air intrusion into the gas collection system or waste mass

Nitrogen (78% of air) and oxygen are not produced by anaerobic decomposition; elevated levels indicate atmospheric air is being drawn into the collection system, which dilutes LFG, reduces energy value, and can create explosive gas mixtures.