Title: The Role of Landfill Gas Emission Rate Calculation Methods in Solid Waste Landfill Risk Assessments
1The Role of Landfill Gas Emission Rate
Calculation Methods in Solid Waste Landfill Risk
Assessments
- Sarah A. Foster
- Paul C. Chrostowski, Ph.D.
- CPF Associates, Inc.
- Steve Wilsey
- Conestoga Rovers Associates, Inc.
- Society for Risk Analysis
- 2006 Annual Meeting
- December 2006
- Baltimore, Maryland
2Introduction
- MSW landfills
- Dominant disposal method in many countries
- Roughly 55 of US MSW
- Common community concerns
- Health risks from landfill gas
- Cancer and noncancer health effects
- Odors
- Risk assessments
- Can be used to help evaluate community health
concerns
3Presentation Outline
- What is landfill gas?
- Methods for calculating landfill gas emission
rates for use in risk assessments - Case studies
- Conclusions
4What is Landfill Gas (LFG)?
- By-product of biodegradation of municipal solid
waste - 45-60 methane
- 40-60 carbon dioxide
- lt1 trace compounds including volatile organic
compounds and sulfur-containing compounds
5Overview of Landfill Gas Emission Sources
Total gas generated
Uncollected gas
Gas collection system
Landfill surface (cover, fissures)
Treatment devices (flare, gas-to-energy
6Methods for Calculating Landfill Gas Emission
Rates
- Modeling
- Total gas generation rate
- Gas system collection efficiency
- LFG composition
- Calibration using site-specific data
- Measured gas collection rates
- Measured LFG composition
- Measured versus modeled downwind ambient air
levels - Measurement
- Surface flux boxes
- Optical remote sensing methods (emerging, limited)
7Case Studies LFG Emission Sources
8Landfill 1 LFG Emissions and Dispersion
- Modeled emission rates
- EPA LANDGEM model
- Default inputs
- Used 70-year average gas generation rate
- Assumed gas collection efficiency (75)
- LFG concentrations
- Site-specific gt Waste Industry Air Coalition
averages gt EPA AP-42 - SCREEN3 dispersion model
- Modeled as one area source
- Evaluated assumed residential locations
100 m - 2,500 m from landfill
9Landfill 2 LFG Emissions and Dispersion
- Measured emission rates
- EPA surface flux box sampling method
- 8 flux box samples
- Analyzed for VOCs and sulfur compounds
- ISCST3 dispersion model
- Modeled as four area sources (active cover,
interim cover, final cover, 1 fissure) - Evaluated 15 nearby residential locations
10Landfill 3 LFG Emissions
- Modeled emission rates
- EPA LANDGEM model
- Calibrated to site-specific gas collection rates
- Assumed gas collection efficiency (90)
- Site-specific LFG concentrations
- Calibrated H2S emission rate using
surface air measurements - Jerome H2S analyzer
- 94 surface measurements
11Landfill 3 H2S Surface Emission Rates
- Measured 0.004 ppm
- Modeled 0.7 ppm (simple box model)
- Modeled concentrations 175 times gt measured
concentrations - Reduced H2S emission rate by scaling factor of
100
4
12Landfill 3 LFG Dispersion Modeling
- ISCST3 Dispersion model
- Modeled as 3 area sources
- Calculated average concentrations in 3
surrounding areas
13Landfill 4 LFG Emissions
- Measured emission rates
- EPA surface flux box sampling method
- 18 flux box samples
- Analyzed for VOCs and sulfur compounds
14Landfill 4 LFG Dispersion Modeling
- ISCST3 Dispersion model
- Modeled as 4 area sources
- Calculated average
concentrations in 2 nearby residential areas
15Landfill 5 LFG Emissions and Dispersion
- Vinyl chloride only
- Modeled emission rates
- EPA LANDGEM model
- Initial Default inputs
- Refinement
- Site-specific calibration compared measured
versus modeled ambient air concentrations at
downwind sampling locations - Reduced all emission rates by factor of 2.5
- FDM dispersion model
- Modeled as 4 area sources
- Evaluated residential locations within 1 km
16Landfill 5 - Model Calibration
Source RWDI 1999
17Case Study Risk Assessment Results
- Solid, non-hazardous waste landfills equipped
with LFG collection and treatment systems - Used variety of methods to calculate landfill gas
emission rates - Long-term and short-term risks associated with
LFG compounds below regulatory and risk-based
target levels - Excess lifetime cancer risks 3x10-9 1x10-6
- Noncancer hazard index values 0.0005 0.1
- Surface area emissions dominated inhalation risk
results
18Modeling LFG Emission Rates - Uncertainties
- Landfill gas generation models can overestimate
emissions - Gas generation model does not take into account
cover effects - Model based on methane NMOC releases may not be
correlated with methane production - Defining LFG concentrations
- Gas collection efficiency
19Conclusions and Future Research
- Tiered approach - tailor to project scope
- Hierarchy
- Measurement (flux box)
- Modeling with site-specific calibration
- Modeling with some site-specific data
- Research areas
- Attenuation effects of landfill gas covers
- Validation of landfill gas generation and
emission models - Validation of modeled off-site concentrations
using measured ambient air data
Increasing uncertainty