CPWM Landfill Gas Management and Energy Recovery 2 — Questions and Answers
Question 1: What is the primary regulatory purpose of a gas collection and control system (GCCS) at a municipal solid waste landfill?
- To prevent rainwater infiltration into the waste mass
- To capture and control LFG emissions to meet Clean Air Act requirements (Correct answer)
- To accelerate the rate of waste decomposition
- To monitor groundwater quality beneath the landfill
Correct answer: To capture and control LFG emissions to meet Clean Air Act requirements
A GCCS is required under the Clean Air Act to collect LFG and route it to a control device (flare or energy recovery system) to prevent uncontrolled release of methane and non-methane organic compounds.
Question 2: Under 40 CFR Part 60 Subpart Cf, at what non-methane organic compound (NMOC) emission rate must a landfill install a gas collection and control system?
- 10 megagrams per year
- 25 megagrams per year
- 34 megagrams per year (Correct answer)
- 50 megagrams per year
Correct answer: 34 megagrams per year
Under the 2021 EPA rule (40 CFR Part 60 Subpart Cf), landfills must install a GCCS when the calculated NMOC emission rate equals or exceeds 34 megagrams per year.
Question 3: Which of the following best describes 'renewable natural gas' (RNG) produced from a landfill?
- Natural gas piped to the landfill to power heavy equipment
- LFG purified to pipeline-quality methane content for injection into the natural gas grid (Correct answer)
- Compressed natural gas produced on-site to fuel collection vehicles directly
- Biogas generated from an on-site composting operation adjacent to the landfill
Correct answer: LFG purified to pipeline-quality methane content for injection into the natural gas grid
RNG (biomethane) is LFG that has been processed to remove CO2, water, hydrogen sulfide, and other impurities until it meets the methane content and quality standards required for injection into the natural gas distribution system.
Question 4: Which EPA tool is the standard model used for estimating landfill gas generation rates and total emissions from MSW landfills?
- HELP Model (Hydrologic Evaluation of Landfill Performance)
- LandGEM (Landfill Gas Emissions Model) (Correct answer)
- MODFLOW groundwater flow model
- SWMM (Storm Water Management Model)
Correct answer: LandGEM (Landfill Gas Emissions Model)
EPA's LandGEM model uses first-order decay equations to estimate methane generation rates, NMOC emissions, and other LFG constituents over time based on waste acceptance rates.
Question 5: What minimum destruction or removal efficiency must an enclosed combustion device achieve for NMOCs under EPA regulations for MSW landfill gas?
- 85% destruction efficiency
- 95% destruction efficiency
- 98% destruction efficiency (Correct answer)
- 99.9% destruction efficiency
Correct answer: 98% destruction efficiency
EPA regulations require enclosed combustion devices treating LFG to achieve a minimum 98% destruction or removal efficiency for non-methane organic compounds.
Question 6: What term describes the subsurface horizontal movement of landfill gas through soil into adjacent properties or structures?
- LFG percolation
- LFG lateral migration (Correct answer)
- LFG volatilization
- LFG efflorescence
Correct answer: LFG lateral migration
Lateral migration of LFG occurs when methane travels horizontally through subsurface soils away from the landfill, potentially reaching explosive concentrations inside adjacent buildings and structures.
Question 7: Which of the following is NOT a common beneficial use pathway for landfill gas energy recovery?
- Electricity generation via internal combustion engines or turbines
- Direct use as boiler fuel for industrial or institutional heating
- Upgrading to pipeline-quality RNG for injection into the gas grid
- Direct use as aviation jet fuel for commercial aircraft (Correct answer)
Correct answer: Direct use as aviation jet fuel for commercial aircraft
Aviation jet fuel requires highly refined hydrocarbon fuels with specific energy density and combustion properties that LFG cannot provide; common LFG energy uses are electricity generation, direct thermal use, and RNG production.
CPWM Landfill Gas Management and Energy Recovery 2
What is the primary regulatory purpose of a gas collection and control system (GCCS) at a municipal solid waste landfill?