CLIMATE LEADERS GREENHOUSE GAS INVENTORY PROTOCOL
CORE MODULE GUIDANCE
Direct Emissions from
Municipal Solid Waste
Land-filling
CLIMATED
U.S. Environmental Protection Agency
October 2OO4
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The Climate Leaders Greenhouse Gas Inventory Protocol is based on the Greenhouse Gas Protocol (GHG Protocol)
developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development
(WBCSD). The GHG Protocol consists of a corporate accounting and reporting standard and separate calculation
tools. The Climate Leaders Greenhouse Gas Inventory Protocol is an effort by EPA to enhance the GHG Protocol to fit
more precisely what is needed for Climate Leaders. The Climate Leaders Greenhouse Gas Protocol consists of the
following components:
• Design Principles Guidance
• Core Modules Guidance
• Optional Modules Guidance
All changes and additions to the GHG Protocol made by Climate Leaders are summarized in the Climate Leaders
Greenhouse Gas Inventory Protocol Design Principles Guidance.
For more information regarding the Climate Leaders Program, visit us on the web at www.epa.gov/climateleaders
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M S W Landfill Sources — Guidance
1. Introduction 1
1.1. Gases Included 1
1.2. Sources Included 2
2. Methods for Estimating CH4 Emissions 4
2.1. Estimating Landfill Methane Emissions at MSW Landfills without
Active Gas Collection Systems 4
2.2. Estimating Landfill Methane Emissions at MSW Landfills with
Active Gas Collection Systems 6
2.3. Estimating Methane Emissions from a Continuous Emissions
Monitoring System (CEMS) 10
2.4. Bioreactor Landfills 10
3. Choice of Methods 11
4. Solid Waste Input Activity Data and Emission
Calculation Factors 12
4.1. Solid Waste Input Activity Data 12
4.2. Emission Factors Data 13
5. Completeness 16
6. Uncertainty Assessment 17
7. Reporting and Documentation 18
8. Inventory Quality Assurance and Quality Control 19
Appendix A. LandGEM Sample Output 2O
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Introduction
This document presents guidance for estimating
direct greenhouse gas (GHG) emissions from
owned/operated municipal solid waste landfill
sites. This guidance applies to any company whose
operations involve municipal solid waste landfilling.
Sanitary landfilling is one of the primary methods of
disposing of municipal solid waste (MSW) and has
been an accepted solid waste management practice for
many decades. In 2000, an estimated 128.3 million tons
(or 116 million metric tonnes), representing approxi-
mately 55.3 percent of the reported 231.9 million tons
(or 210.5 million metric tonnes) of MSW generated
within the United States was managed through landfill-
ing1. A direct result of solid waste landfilling is the
generation of a natural by-product known as landfill
gas (LFG) which is formed through the biodegradation
of the decomposable organic fraction of the MSW land-
filled. The gas is generally composed of 30 to 60
percent methane (CH4) depending on a number of fac-
tors with the balance primarily carbon dioxide (C02).
Other minor constituents present in the gas can
include oxygen and nitrogen, trace amounts of hydro-
gen, hydrogen sulfide, volatile organic compounds
(VOCs), and moisture. Depending on site characteris-
tics, the LFG generation process can create internal
positive pressure within the waste mass allowing
for the fugitive emission of produced gas through
permeable areas or pathways of least resistance within
the final and temporary cover systems, leachate collec-
tion system and risers, landfill side slopes, etc.
Sources of GHG emissions from municipal solid waste
landfilling include the fugitive release of landfill gas as
well as stationary combustion sources, such as LFG
flares and LFG energy (LFGE) facilities. Additional
sources of GHG emissions include; fleet vehicles,
landfill compactors, earthmovers and other equipment
or machinery that is a necessary or typical part of the
landfill operation that uses fossil fuels.
1.1. Gases Included
Although CH4, C02, and minor trace gases are all
emitted from fugitive landfill gas release, methane
accounts for the majority of GHG emissions from MSW
landfills2. MSW landfills are the largest human-made
source of CH4 emissions in the U.S. Landfill gas is made
up of approximately equal amounts (on a volumetric
basis) of CH4 and C02 gas, however, only CH4 is
addressed within this protocol. The C02 produced
through the anaerobic biodegradation of MSW
(C02 fraction of LFG) is not reported. It is assumed
that waste decomposition does not contribute to the
net addition of C02 to the atmosphere. This exclusion
is consistent with Intergovernmental Panel on Climate
Change (IPCC) guidance3.
1 U.S. EPA. Municipal Solid Waste in The United States: 2000 Facts and Figures. 2000 Update; EPA530-R-02-001.
2 In landfills, some carbon from waste can remain stored for long periods of time. The removal of carbon from the natural cycling of carbon between the
atmosphere and biogenic materials - which occurs when wastes of biogenic origin are deposited in landfills - sequesters carbon. (Wastes of biogenic
origin include paper, wood products, and yard trimmings, but do not include plastics or other synthetic organics) When wastes of sustainable, biogenic
origin are landfilled, and do not completely decompose, the carbon that remains is effectively removed from the global carbon cycle. While EPA is con-
tinuing to study methodologies to measure this type of carbon storage, currently considerable uncertainty remains and thus Climate Leaders does not
include this process in its GHG accounting.
3 "Decomposition of organic material derived from biomass sources (e.g., crops, forests) which are regrown on an annual basis is the primary source of
C02 released from waste. Hence, these C02 emissions are not treated as net emissions from waste in the IPCC Methodology." Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories: Reference Manual, Chapter 6. Waste, Section 6.1 Overview, pg. 6.1.
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M S W Landfill Sources — Guidance
C02 can also be produced from the combustion
of CH4 in captured LFG, this is considered
biomass C02. As with emissions from other
biofuels combustion, Climate Leaders consid-
ers that biomass C02 emissions do not
contribute to C02-equivalent emissions as
reported in a Climate Leaders Partner's entity-
wide inventory4. Therefore, the biomass C02
emitted through the combustion of captured
LFG are reported but only as a memo item in
the Partner's inventory. Climate Leaders
Partners are required to account for emissions
of methane from MSW landfill sites.
1.2. Sources Included
This guidance covers emissions associated
with LFG. When considering LFG emissions
there are different factors to be taken into
account including; production of the LFG,
recovery of the gas, and treatment of the gas
as shown in Figure 1.
Figure 1: Scope of Emissions Covered in This Guidance
= Included in this Guidance
LFG Generated
\Collection
System I
Efficiency /
CH4 Oxidation in Cap
Vented ' ri/n On-Site Electricity/
CH4 Emissions (on-or off-site) 1 t-iared/uirect use steam Generation
I [Sold Off-Site 1 1
CH4 Emissions i CO2 (biomass) CO2 (biomass)
1 Emissions Emissions
CH4 Sold
Electricity/
" Steam Sold
4 This assumes no net loss of biomass-based carbon associated with the land use practices used to produce these fuels. This
approach is consistent with that used by the U.S. EPA in conducting the National Inventory, U.S. EPA 2004 Inventory of U.S.
Greenhouse Gas Emissions and Sinks: 1990-2002, EPA430-R-04-003, April 2004. Also,"C02 emissions from landfill gas recovery com-
bustion are of biogeneic origin and should not be included in National Totals." IPCC Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories, Chapter 5. Waste, Section 5.1.1.2, Methane Recovery pg. 5.10.
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M S W Landfill Sources — Guidance
As mentioned in Section 1.1, projects using LFG
as a fuel in stationary or mobile sources report
the biomass C02 emissions from the combus-
tion of LFG (oxidation of carbon in the LFG) as
a memo item in the inventory5. Methods for
estimating emissions from combustion of LFG
are covered under additional Climate Leaders
guidance. Carbon dioxide emissions resulting
from a flare or an LFG (or LFG supplemented)
electrical power generation station are calcu-
lated according to the Climate Leaders
guidance for Direct Emissions from Stationary
Combustion Sources. Emissions resulting from
liquid or compressed fuels derived from LFG
used in a Climate Leaders Partner's truck or
vehicle fleet are calculated according to the
Climate Leaders guidance for Direct Emissions
from Mobile Combustion Sources. Furthermore,
any additional sources of emissions from land-
fill operations, for example, combustion of
fossil fuel in mobile sources or purchases of
electricity, are also reported separately using
the appropriate Climate Leaders guidance.
Climate Leaders Partners are only responsible
for direct emissions at their facilities. If carbon
is sold and leaves the facility stored in a prod-
uct it should not be counted as a release even
if the product is subsequently burned or other-
wise releases
the stored carbon.
In addition to reporting of direct emissions,
there is also the potential that landfills can
report savings due to collection and treatment
of CH4 that would otherwise have been
released to the atmosphere. Guidance for
reporting these reductions is currently under
development.
5 This assumes carbon in LFG is of biogeneic origin and that there is no net loss of biomass-based carbon associated with land use
practices surrounding the biomass that ultimately decomposes in the landfill to produce the LFG.
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M S W Landfill Sources — Guidance
Methods for Estimating CH4
Emissions
In general, there are two approaches used potential (L0), and the methane generation
to estimate CH4 emissions from MSW land- rate constant (k) to estimate potential annual
fills, depending on the presence or absence emission rates from landfill sites. The
of a gas recovery and control system. LandGEM is based on Equation 1.
• MSW landfill sites in which gas collection
systems are absent: use mathematical
models and apply appropriate default
factors (see Section 2.1).
• MSW landfill sites with landfill gas recovery
and control systems: monitor recovered
landfill gas and apply gas system collection
efficiency data (see Section 2.2).
2.1. Estimating
Landfill Methane
Emissions at MSW
Landfills without
Active Gas Collection
Systems
Through the Control Technology Center, the
U.S. EPA has developed an emissions model
known as the "Landfill Gas Emissions Model" or
LandGEM. The model is a tool used to estimate
annual emission rates over a user-specified
interval for methane as well as carbon dioxide,
non-methane organic compounds (NMOC), and
a list of other air pollutants. The LandGEM
model has been implemented within a stand-
alone software application distributed and
supported by the U.S. EPA.
The model uses a first-order decay rate equa-
tion and operator-entered data for annual
reported MSW tonnage, methane generation
Equation 1: Waste
Decomposition Model
where:
QCH4
k
M,
methane emission rate, m3/yr
methane generation rate
constant, year1
methane generation poten-
tial, m3 of CH4/Mg of refuse
mass of the waste in the ith
section (annual increment),
Megagrams (Mg)
age of the ith increment (or
section), in years
This equation computes the methane emission
rate from one annual increment of waste where
Mj is the mass in Megagrams (Mg) (or metric
tonnes) of the annual waste increment and ts is
the age of the ith increment, in years. The mass
of any non-MSW may be subtracted from the
total waste mass in a particular section when
calculating the value for the mass of waste
in that section. The methane emission rates
are summed over all past annual increments
to estimate the total current methane
emission rate, which is further represented
in Equation 2.
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M S W Landfill Sources — Guidance
Equation 2: Summation of
Annual Emission Rates
Q
CH4
1=1
where:
QCH4
k
M,
methane emission rate, m3/yr
methane generation rate
constant, year1
methane generation poten-
tial, m3 of CH4/Mg of refuse
mass of the waste in the fh
section (annual increment),
Megagrams (Mg)
age of the th increment (or
section), in years
The estimates of landfill methane emissions
from the model only consider methane genera-
tion and not landfill methane released to the
atmosphere. As shown in Figure 1, not all LFG
that is generated gets released to the atmos-
phere. A portion of the methane generated may
be oxidized while passing through the landfill
cover, through soils used for daily cover, and
through alternative cover materials such as
compost used for odor control in, or on, land-
fill covers. Landfill methane emissions from
sites without active LFG recovery systems are
equal to the methane generation less the
amount of methane oxidized based on the
above potential oxidizing sources.
Based on the site size and gas management
practiced, some landfills may have installed
passive controls (wells, horizontal collectors
and/or trenches) which simply vent collected
gas to the atmosphere. Passive controls rely
on the gas generation and internal pressure
created within the waste mass to move the gas
through diffusion and/or convection to the
atmosphere. To date, there are no industry
standard accepted collection efficiencies for
passive LFG venting systems. If the methane
emissions resulting from a passive venting sys-
tem are measured, the emissions are a fraction
of the overall gas emission estimated using the
gas generation model. Passive controls may
reduce the potential for methane to be oxi-
dized.
Equation 3 describes the calculation to convert
methane generated into methane emissions,
default values for factors used are provided in
Section 4.2.
Equation 3: Estimating CH4 Emissions
Based on Generation
CH4 Emissions = CH4 generated x (1 - oxidation factor)
The methodology used to determine methane
emissions from MSW landfills through the gas
generation method is as follows and assumes no
active or passive gas control is implemented:
Step 1: Determine the landfill methane gen-
eration rate. This is done using the
LandGEM model as described above and
following the user manual to enter
required landfill and model data and step
through the program. Input data include
Mg (metric tonnes) per year of municipal
solid waste accepted and buried, the year
the landfill opened, the current year, land-
fill design capacity, landfill closure year,
and waste in place. Input data includes
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M S W Landfill Sources — Guidance
the methane generation potential (L^, the
methane generation rate constant (k) and
selected methane concentration. A
Climate Leaders Partner may also make
these calculations directly using the first-
order decay equations that are the basis
of the LandGEM model if so desired.
Step 2: Determine the fraction of methane
oxidized. Landfill gas may pass through
the landfill cover, intermediate cover soils
or alternative cover materials (compost)
before being released to the environment.
There is the potential that microbes in
the soil or cover material may oxidize
some of the methane in the gas. This oxi-
dation reduces the amount of methane
released to the environment. The Climate
Leaders approach is to use a default fac-
tor of 10/6 for the fraction of methane
oxidized. Refer to Section 4.2 for discus-
sion of default parameters.
Step 3: Calculate methane emissions. Once
the above parameters are known
Equation 3 can be used to determine
amount of methane emissions. Methane
emission rates have to be converted from
volume to mass through a simple conver-
sion calculation based on the assumed
density of methane.
Note: If the Climate Leaders Partner proposes
to use measured flow rates from a passive
gas collection and venting system to deter-
mine the net methane emission based on
the collection efficiency of the passive sys-
tem, a methodology must be presented for
determining the passive collection efficien-
cy. There is no widely accepted method for
doing so. Therefore this approach has not
been considered in the above methodolo-
gy or the example for estimating methane
emission from MSW landfills without active
LFG collection systems.
2.2. Estimating
Landfill Methane
Emissions at MSW
Landfills with Active
Gas Collection
Systems
Methane generation at MSW landfills with
active gas collection systems (that is, incorpo-
rating gas collection systems used to extract
LFG under an induced vacuum applied to the
recovery wells and collection system) could be
estimated using data from the gas collection
system, verified by a qualified third party using
U.S. EPA verification methods, and applying a
collection system efficiency suitable to the site
specific nature of the landfill cover system and
gas collection system installation. The differ-
ence between the methane gas generation
calculated in this manner and the measured
methane gas recovery from the gas collection
system (less the amount of methane oxidized
within the final cover system) plus any vented
gas is the net methane emission to the atmos-
phere. Equation 4 describes the calculation to
convert amount of collected methane into
methane emissions.
The methodology used to determine methane
emission data from MSW landfills through the
active gas collection method is as follows,
default factors are provided in Section 4.2:
Step 1: Determine the amount of methane
collected. Landfill gas collection and/or
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Example CH4 Emissions Calculation for MSW Landfills
without Active LFG Collection
A Climate Leaders Partner owns a MSW Landfill Site which has been receiving primarily domestic waste for the past 20 years
and is still active (year opened 1982). Under the NSPS regulations the Partner has not yet been required to install a LFG control
mechanism. The landfill site has a permitted capacity of 3 million cubic meters and has annual waste acceptance records from
the time of opening. Average waste compaction density is 0.8 tonnes/m3 (1,350 lb/yd3). The site is located in a very dry climate
receiving less than 635 mm (25 inches) of precipitation per year. The Partner has not assessed methane emissions previously at
the site.
The Partner uses the Landfill Gas Emissions Model (LandGEM Version 2.01) to calculate the methane emissions using the AP-42
default factors for the methane generation potential (L0 = 100 m3 of CH4/Mg of MSW landfilled) and methane generation rate con-
stant (k = 0.02/yr). The final cover system is one meter of clay and topsoil and does not have a flexible membrane liner.
Step 1 - Estimate current methane generation rate using the LandGEM (Version 2.01):
Model Inputs:
Waste disposal = annual tonnage of MSW for each filling year (Mg)
L0 = AP-42 default (100 m3/Mg)
k = AP-42 default (arid 0.02/yr)
Design capacity in Mg (or metric tonnes), year landfill opened and current year
Methane concentration = 50% by volume
LandGEM output yields a methane emission rate in both mass (Mg) and volume (m3) on an annual basis. Conversion from the
volumetric to a mass emission rate of methane is achieved through the use of the density of methane. The LandGEM Model
assumes a density of methane at 1 atmosphere and 20°C, which is equal to 0.667 kilograms/cubic meter (0.0416 lb/ft3). A sample
report generated using LandGEM 2.01 is presented in Appendix A using the above parameters and an average annual waste
acceptance of 80,000 Mg/yr.
Note: If the annual waste acceptance is unknown for any increment or interval, then the average annual waste acceptance
should be used accordingly.
Step 2 - Determine the fraction of methane oxidized:
The methane oxidation factor is assumed to be 10% by volume (0.10). (see Section 4.2)
Step 3 - Calculate emissions:
This is done using the parameters specified above and Equation 3 outlined in Section 2.1
CH4 Emissions = CH4 generated x (1 - oxidation factor)
For the year 2003:
CH4 generated = 1.85 x 103 tonnes (or Mg)/yr. (from the LandGem output shown in Appendix A)
CH4 Emissions = 1.85 x 103 x (1 - 0.10) = 1.66 x 103 metric tonnes of CH4 emitted in 2003.
Note: Emissions from any on-site combustion device are calculated using the Climate Leaders guidance for Direct Emissions
from Stationary Combustion Sources. Emissions from these calculations, along with any other emissions sources, are added to
the total emissions of the site.
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Equation 4: Estimating CH4 Emissions Based on Collection
CH4 Collected
CH4 Emissions = [( —- CH4 Collected) x (1 - OF)] + (CH4 Collected x Vent)
where:
Coll
eff
OF
Vent
Coll
eff
CH4 Collected = CH4 Collected by active gas collection system
collection system efficiency
oxidation fraction
fraction vented
combustion systems generally are
equipped with LFG composition and flow
monitoring equipment which can be used
to continually monitor methane capture
from the landfill. In the event flow and
composition data are not continuously
monitored, routine gas sampling and flow
measurement using portable monitoring
equipment with data recording capability
could be used, providing data can be sup-
ported through third party verification
methods.
Step 2: Determine the collection system effi-
ciency. With a gas collection system in
place there may still be some fugitive gas
that is not collected by the system. This
could be due to spacing of gas collection
wells, gas pressure, maintenance of the
cover, etc. Refer to Section 4.2 for default
selection of suitable collection system
efficiency to be used.
Step 3: Determine the fraction oxidized.
Landfill gas that is not collected passes
through the landfill cover before being
released to the environment. There is the
potential that microbes in the soil of the
landfill cover oxidize some of the methane
in the gas. This oxidation reduces the
amount of methane released to the environ-
ment. The Climate Leaders approach is to
use a default factor of 10% for the fraction
of methane oxidized. Refer to Section 4.2
for discussion of default parameters.
Step 4: Determine the fraction of gas vented.
This is the amount of the collected gas that
is vented directly to the atmosphere. It
could either be through an active venting
system, or in some cases gas may also be
vented during scheduled start-up/shut
down periods as well as from a malfunction
of the primary LFG control device.
Estimates should be made for LFG control
device downtime if gas is vented during
that period.
Step 5: Calculate methane emissions. Once all
the parameters are known, Equation 4 can
be used to determine the amount of
methane emissions. Methane emission
rates can be converted from volume to
mass through a simple conversion
calculation based on the density of
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Example CH4 Emissions Calculation based on Collection
A Climate Leaders Partner has a MSW Landfill Site which has been receiving waste for the past 15 years and is still active. Based
on meeting criteria under the NSPS regulations, the Partner has installed a LFG collection and enclosed flaring system. The land-
fill site has been receiving 300,000 tonnes (Megagrams) of MSW per year and the site is located in a temperate climate receiving
greater than 635 millimeters (25 inches) of precipitation per year. The partner has assessed methane and non-methane organic
compound emissions previously at the site using the Landfill Gas Emissions Model with the required defaults for NSPS report-
ing. All LFG collected is flared at the site and the gas collection system is currently thermally destroying a consistent average of
1,000 standard cubic feet per minute (scfm) of LFG with a methane concentration of 53% by volume. The landfill is a currently
active with 5 years of operation remaining and will be eventually closed with a low permeability clay cover.
Step 1 - Determine the amount of methane collected:
1,000 ft3/minx 0.53
CH, collected/year = x 525,600 minutes/year
4 35.31 ft3/m3
7.89 x 106 m3/yr
Step 2 - Determine the collection system efficiency:
The collection system efficiency is assumed to be 75% by volume (0.75). (see Section 4.2)
Step 3 - Determine the fraction of methane oxidized:
The fraction oxidized is assumed to be 10% by volume (0.10). (see Section 4.2)
Step 4 - Determine the fraction of methane gas vented:
Flare station records indicate that approximately 1% (0.01) of the recovered gas is vented during routine and
unscheduled maintenance annually. These estimates should be made for flare system downtime if gas is vented during
that period.
Step 5 - Calculate methane emissions:
CH4 emissions = [((CHj collected/collection system efficiency) - CH4 collected) x (1-oxidation factor)] +
[CH4 collected x fraction vented]
CH4 emissions = [((7.89 x 1$ m3/yr/0.75) - 7.89 x 106 m3/yr) x (1 - 0.10)]+ [7.89 x 106 m3/yr x 0.01]
[2.63 x 106 m3/yr x 0.90] + 7.89 x 104 m3/yr
2.45xl06m3/yr
Note: Conversion from the volumetric to a mass emission rate of methane is achieved through the use of the density of
methane. The density of methane is equal to 0.667 kilograms/cubic meter (0.0416 lb/ft3) at 1 atmosphere and 20°C.
QCH4 tonnes/yr. = 2.45 x 106 m3/yr. x 0.667 kg/m3 x 1 tonne/1000 kg = 1,634 tonnes/yr.
Note: The latest version of LandGEM as described in the previous section and sample calculation is used to estimate the
methane emission rate in the area not served by the landfill gas collection system, as applicable. Also, emissions from any on-
site combustion device would be calculated using the Climate Leaders guidance for Direct Emissions from Stationary Combustion
Sources. Emissions from these calculations, along with any other emissions sources, are added to the total emissions of the site.
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methane at standard temperature and
pressure conditions.
The method of estimating landfill methane
emissions at MSW sites incorporating LFG
collection systems described in this section
should be used only for landfill cells or landfill
areas being served by the gas collection sys-
tem. Estimation of landfill methane emissions
for cells or landfill areas not being served or
equipped with active gas recovery systems
should be calculated using LandGEM (Version
2.01), as described in Section 2.1.
2.3. Estimating
Methane Emissions
from a Continuous
Emissions Monitoring
System (CEMS)
Neither the New Source Performance
Standards (NSPS) nor the U.S. Clean Air Act
require continuous monitoring systems for
methane emissions on MSW landfills. However,
the new National Emission Standards for
Hazardous Air Pollutants (NESHAP) for MSW
Landfills require procedures for operating and
maintaining the collection and control system,
including the continuous monitoring system
during periods of start-up, shut-down and
malfunction for LFG active collection systems
on NSPS landfill sites6.
The landfill gas combustion systems generally
are equipped with LFG composition and flow
monitoring equipment which can be used to
continually monitor methane capture from the
landfill. This equipment could potentially be
used to monitor other GHG emissions such as
C02 (biomass), CH4, and nitrous oxide (N20)
from stationary combustion sources (see
Climate Leaders guidance for Direct Emissions
from Stationary Combustion Sources).
2.4. Bioreactor
Landfills
Bioreactor landfills enhance the microbio-
logical process involved within the landfill to
speed up the rate of waste decomposition.
This enhancement can occur through several
means. If the decomposition process is anaero-
bic, methane gas is produced. Estimating
emissions from bioreactor landfills can be done
using one of the methods outlined in this
guidance. The recommended choice of method
is discussed in Section 3. If emissions are to be
estimated based on the Landfill Gas Emissions
Model (described in Section 2.1 Estimating
Landfill Methane Emissions at MSW Landfills
without Active Gas Collection Systems) the
parameters of the model, and potentially the
model itself, are different than for a standard
MSW landfill. Currently there is no good data
on appropriate default factors that could be
used to represent bioreactor landfills in this
approach. More work is needed on this area,
therefore, it is recommended that emissions
from bioreactor landfills be estimated based on
an active collection system approach
(described in Section 2.2) or through CEMS
(described in Section 2.3).
6 40 CFR 63 National Emission Standards for Hazardous Air Pollutants: Municipal Solid Waste Landfills, Final Rule.
1 O
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Choice of Methods
The preferred choice of method used
to estimate emissions depends on the
type of information available. If the site
has a gas collection system in place and has
good data on the amount of gas collected and
the methane concentration in the gas, then
the emission calculation method based on gas
collected is preferred. Using the data gathered
from the LFG collection system is likely to
provide a more precise estimate of net gas
emissions than gas modeling, even if the
estimate of collection efficiency is itself
relatively imprecise.
However, if there is no collection system in
place then the modeling approach is the
preferred method for calculating emissions.
The approaches for measuring or recording the
estimated landfill methane emissions in order
of preference are therefore:
1. Partner has LFG quantity (volume) and
quality (composition) of LFG captured
within the gas collection system at the site.
2. Partner has landfill parameters, waste
composition data and annual waste accept-
ance figures for the site and uses LandGEM.
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M S W Landfill Sources — Guidance
Solid Waste Input Activity Data
and Emission Calculation
This section discusses choices of activi-
ty data and factors used for calculating
landfill methane emissions. This guid-
ance has been structured to accommodate
Partners with varying levels of available
information. Whenever possible, the preferred
approach described within this document for
estimating emissions from MSW landfills with
or without gas collection systems should be
the option employed to allow for the greatest
level of accuracy in the landfill methane
emission estimates.
4.1. Solid Waste Input
Activity Data
When calculating landfill methane emissions
using the LandGEM model, the initial
information required is the type of waste
(historical/current) accepted by the landfill
site and the annual tonnage records, if
available over the life of the landfill. Generally,
depending on the landfill size and age, older
sites will have only minimal filling records
available for the late 1960's up to the early
1980's. In this case, annual tonnage and waste
stream data can be taken as averages over the
years required. If inert material has been
accepted in known quantities and landfilled,
these tonnage data should be subtracted from
the overall annual MSW figures used in the
calculation of the landfill methane emissions.
The next source of data required is the climatic
condition of the site (i.e., arid with less
than 635 millimeters or 25 inches of annual
precipitation, or non-arid with greater than 635
millimeters of annual site precipitation), this
determines what default factor is selected for
the methane generation rate constant. If input
parameters other than defaults are used, site
specific data obtained by gas recovery testing
is the next data source. The minimum site data
which must be reported to conduct a methane
emission estimate is 1) the type of waste and,
2) annual tonnage figures.
When calculating landfill methane emissions
based on gas collected, the main initial source
data required is the volume of LFG annually
captured and measured methane concentration
by volume. This is the preferred method of
estimating landfill methane emissions based on
assumed or calculated gas collection system
efficiency. In the case where a collection
system covers only a portion of the site, a
percent coverage must be used and reflect the
overall area of influence for the gas collection
system. The landfill methane emissions from
large portions of the site and cells not contain-
ing LFG recovery systems and equipment are
estimated separately using measured waste
tonnage data and emission model calculations.
Landfill gas is metered in terms of physical
and chemical units (i.e., mass or volume and
percent methane by volume) and it is recom-
mended that Partners track landfill methane
generation, recovery (including composition
by volume) and emissions to the atmosphere
in terms of these physical and chemical units.
Partners with MSW landfills incorporating gas
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collection should be continuously measuring
gas recovered through gas collection monitor-
ing systems. However, depending on the
consistency of the sustainable volumes of LFG
recovered, Partners may choose to monitor
methane concentration periodically throughout
the year. Quantity of landfill gas for recovery
and methane composition may vary due to
changes in site conditions, gas line blockages,
damage to LFG system from site activities, sys-
tem down time and fluctuations in anaerobic
conditions (resulting from possible air ingres-
sion). For these reasons, it is recommended
that continuous metering and data computa-
tion of LFG volumetric flow rate and methane
concentration is conducted, for emission
reporting accuracy as well as for future
emission reduction verification requirements.
4.2. Emission Factors
Data
A factor that is required for the methane
collected method of calculating emissions is
the LFG collection system efficiency (if one is
installed). Gas collection system efficiency
factors can vary widely depending on the type
of landfill gas collection system (horizontal
versus vertical, or a combination of both),
construction and condition of the landfill
cover, the landfill site characteristics, differen-
tial settlement, moisture, or other factors.
If the landfill is completely served by a gas
collection system, then the waste management
industry assumption has been that a collection
efficiency of 75 percent or greater is typically
achieved.7 This collection efficiency factor is
used as a default by Climate Leaders. Data sup-
porting more precise estimates is not available
and this assumption is likely to provide
estimates that are more precise than using the
LandGEM model for the reasons discussed
within this guidance document.
Over the past several years, many landfills
subject to the New Source Performance
Standards (NSPS) for MSW Landfills
(40 CFR Part 60, Subparts WWW and CC) have
been required to conduct surface sweep
monitoring of landfill emissions. Sites with fully
functional and well-maintained low permeabili-
ty cover systems have been found (indeed are
required) to demonstrate near-zero surface
emissions. Therefore, it is reasonable to
assume that sites subject to the NSPS have a
higher collection efficiency than the above-
mentioned waste management industry
standard assumption. If the Climate Leaders
Partner uses an active collection system
efficiency which is greater than 75% the
methodology and assumptions used to
determine the site specific collection efficiency
shall be reported. Closed NSPS landfills with
impermeable geomembrane covers and active
gas controls are expected to have a collection
system efficiency greater than 90%, based on
the consistent reporting of near-zero surface
emission measurements.
Climate Leaders Partners may own or operate
MSW landfill sites which simply vent small
amounts of LFG to the atmosphere for safety
reasons and/or to prevent lateral subsurface
migration from the landfill. This is frequently
done using passive venting systems such as
final cover gas vent layers, vent wells, horizon-
tal gas migration cut-off trenches, and
under-slab venting systems for on-site build-
ings or structures. There are no standard
7 Compilation of Air Pollutant Emission Factors, AP-42, U.S. EPA, 1998. op.cit. p. 2.4 - 6.
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M S W Landfill Sources — Guidance
collection system efficiencies for passive vent-
ing systems and each emission estimation
using passive systems, and the recovery effi-
ciency applied, are evaluated on a site specific
basis. Effectiveness of passive venting is
generally determined by monitoring methane
concentrations in perimeter soils and at
building or structure foundations.
Another factor to be considered for both
methods of estimating emissions is for
methane oxidized as a result of methane oxi-
dizing bacteria found within the landfill cover
system, intermediate soils and alternative daily
cover systems. Studies have been conducted
which support methane oxidation, however the
rates can vary substantially based on the final
cover composition, thickness and seasonal
variations8. Average oxidation of methane (on
a volumetric basis) in some laboratory and
case studies on landfill covers have indicated
ranges from 10 percent to over 25 percent
with the lower portion of the range being
found in clay soils and higher in topsoils9.
A conservative approach is an assumption
that 10/6 of the non-captured landfill methane
passing through the final cover system or soils
may potentially be oxidized. Methane oxidation
factors can be much higher for intermediate
cover materials such as compost applications.
Due to the uncertainty involved and the lack of
a standard method to determine oxidation rate,
EPA recommends the default factor of 10/6 by
volume methane oxidation for landfills with
low permeability cover systems. Landfill cover
systems incorporating a flexible membrane
liner (FML) within the final cover system have
negligible methane oxidation and the default
oxidation rate for these types of covers is
equal to zero.
Use of the methane generation method of cal-
culating emissions requires use of a first order
decay model, which is the basis of the U.S. EPA
LandGEM computer software. The model has
input parameters used to represent character-
istics of the waste as described in Section 2.1.
The variables k and L0 that determine the rate
of gas production are functions of site-specific
conditions. A set of default values for k and L0
are listed in the U.S. EPA's Compilation of Air
Pollutant Emission Factors, Document No. AP-
42, (1998)10. The L0 factor is a function of the
waste composition and a single default is
provided for typical municipal solid waste.
The k factor is a rate constant that is a func-
tion primarily of the refuse moisture content.
Two default values are listed for this factor,
one for arid regions (less than 635 mm or 25
inches of precipitation per year) and another
for non-arid regions. The AP-42 default values
are listed below.
Parameter AP-42 Default Value
L0 100 m3/t
k 0.04/yr (non-arid area)
0.02/yr (arid area)
8 "Quantifying the Effect of Oxidation on Landfill Methane Emissions". P. Czepiel, B. Mosher, P.M. Crill, and R.C. Harriss. 1996. Journal
of Geophysical Research, Volume 101: 16712-16729.
9 "Isotopic signatures of atmospheric methane at NIGEC tower sites and of anthropogenic sources of methane to the atmosphere ".
Annual Progress Report for FY 97/98, National Institute of Global Environmental Change.
10 Compilation of Air Pollutant Emission Factors, AP-42, 5th Edition, Volume 1: Stationary Point and Area Sources Chapter 2: Solid
Waste Disposal, Section 2.4, U.S. EPA Supplement E, November 1998. p. 2.4 - 4.
1 4
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These default parameters are based on
average moisture conditions and generally
reflect "dry-tomb" style landfill applications for
various climates. For "bioreactor" type landfills
the methane generation rate constant is gener-
ally high due to the amount of moisture added
to the waste, resulting in a higher production
rate of LFG over a shorter interval of time. Gas
generation rates for bioreactor type landfills
are generally in the order of two to three times
that of dry tomb landfill operations.
It is suggested that Climate Leaders Partners
having MSW landfill sites without gas collec-
tion systems use the LandGEM computer
model (LandGEM Version 2.01) with AP-42
default factors or site specific determined
values for parameters L0 and k. LandGEM 2.01
can be obtained through the U.S. EPA's
Technology Transfer Network (TIN) at:
http://www.epa.gov/ttn/catc/
products. html#software
Partners who are landfill owners may have
collected data to establish site-specific values
of k and L0 for this widely used model of land-
fill gas emissions. These values may be used if
they were derived using methods approved by
U.S. EPA for this purpose. Partners should
make available the data, data collection proce-
dures, and calculations they used in deriving
these site-specific factors for verification if
they are used for estimating landfill methane
emissions.
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M S W Landfill Sources — Guidance
Completeness
In order for a Partner's GHG corporate
inventory to be complete it must include
all emission sources within the company's
chosen inventory boundaries. See Chapter 3 of
the Climate Leaders Design Principles for
detailed guidance on setting organizational
boundaries and Chapter 4 of the Climate
Leaders Design Principles for detailed guidance
on setting operational boundaries of the corpo-
rate inventory.
On an organizational level the inventory should
include emissions from all applicable facilities.
Completeness of corporate wide emissions
can be checked by comparing the list of
facilities included in the GHG emissions
inventory with those included in other
emission's inventories/environmental report-
ing, financial reporting, etc.
At the operational level, a Partner should
include all emission sources from the facilities
included in their corporate inventory. For a
Partner who's operations include MSW landfill-
ing, possible emissions sources are stationary
fuel combustion, combustion of fuels in mobile
sources, purchases of electricity, HFC emis-
sions from air conditioning equipment and
methane emissions from MSW decomposition.
Partners should refer to this guidance docu-
ment for calculating methane emissions from
MSW decomposition and to the Climate
Leaders Core Guidance documents for calculat-
ing emissions from other sources.
Partners should be aware when using this guid-
ance that any losses in methane collected
based on fugitive emissions through piping sys-
tems should be accounted for. Landfill gas
could be lost due to fugitive releases of LFG
from collection system valves and piping as
well as through the leachate collection system
(LCS). It should be noted that the leachate col-
lection system can be a significant pathway for
landfill methane emissions. Generally most LFG
collection systems installed incorporate provi-
sions for recovery of gas from the LCS piping
and storage network.
As described in Chapter 1 of the Climate
Leaders Design Principles, there is no materiali-
ty threshold set for reporting emissions. The
materiality of a source can only be established
after it has been assessed. This does not nec-
essarily require a rigorous quantification of all
sources, but at a minimum, an estimate based
on available data should be developed for all
sources.
The inventory should also accurately reflect
the timeframe of the report. In the case of
Climate Leaders, the emissions inventory is
reported annually and should represent a full
year of emissions data.
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Uncertainty Assessment
Uncertainties in estimating methane
emissions from MSW landfill sites
without gas collection systems is
high based on the fact the landfill is not a
homogeneous mass of waste deposited under
fully controlled conditions.
The emission estimates using the first-order
decay equation with standard default factors
could have a +/- error of 200% or more depend-
ing on actual site conditions11. There is always
a level of uncertainty in the accuracy of meas-
urements or estimates of the annual landfilled
waste mass, including the variability in the
waste composition. A very important factor
in modeling landfill gas emissions is the under-
lying assumption that the waste composition is
typical (which is generally not the case).
Gas generation and subsequent emission of
that gas to the atmosphere is based on many
factors as discussed throughout this docu-
ment. Also, the first-order decay equation
does not take into account a lag period from
initial placement of waste and assumes gas
generation commences within the first year of
waste placement. Experience with gas collec-
tion from landfills in arid locations shows that
they can exhibit extremely long lag times from
the initial placement of waste until the onset of
significant anaerobic gas production.
Uncertainties associated with estimating land-
fill methane emissions are lessened using
recovery data available from MSW landfills
incorporating a gas collection system.
Assuming that a properly designed gas
recovery system falls in a typical range for gas
collection system efficiency, the confidence
level is higher when back calculating the
landfill methane emissions using default or site
specific gas collection system efficiencies then
the confidence level obtained using the first-
order decay equation.
The area of methane oxidation is not fully
defined and even using a 10 percent methane
oxidation factor can lead to uncertainty in
annual emission estimations calculated and
subsequently reported.
11 Ibid, p. 2.4-4.
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M S W Landfill Sources — Guidance
Reporting and Documentation
Partners are required to complete the
Climate Leaders Reporting Requirements
and report annual emissions. In order
to ensure that emissions estimates are
transparent and verifiable, the input data
used to develop the emission estimates should
be clearly documented and all sources listed in
Table 1 should be maintained for each
relevant year. These documentation sources
should be collected to ensure the accuracy
and transparency of the related emissions data,
and should also be reported in the Partner's
Inventory Management Plan (IMP).
Data
Table 1: Documentation Sources for
Solid Waste Landfill Methane Emissions
Documentation Source
Total permitted landfill capacity
Operating Certificate or Permit
Year opened
Landfill site records
Year of closure
Operating Certificate or Permit, site records
Current area devoted to landfilling
Current contour maps and filling plans
Annual landfill acceptance rate for the site
Tonnage figures including waste in place
Weigh scale records, volumetric calculations,
aerial photographs, and landfill annual reports
MSW composition (% MSW, other organic
wastes, C&D, Fill)
Waste categorization based on weigh scale
records including reused and recycled material
broken down by percent, mass or volume.
Average Waste moisture content
Waste records, climate data
Average Waste Depth
Up-to-date contour map, site records.
Meteorological data, primarily precipitation
Local weather authority or on-site meteorological
station
LFG flow rate and composition
Site testing, Gas collection monitoring system,
flow meter, in-line chromatograph or gas analyzer,
third party laboratory analysis
Landfill area covered by gas collection system LFG system record drawings
Emission factors and default input methane
emission model parameters
All applicable sources, U.S. EPA with programs such as
the Landfill Methane Outreach Program (LMOP), also
SWANA technical documents
Landfill gas captured, flared and/or utilized
Gas collection monitoring system, flow meter, in-line
chromatograph or gas analyzer, third party laboratory
analysis
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M S W Landfill Sources — Guidance
Inventory
Quality Control
Assurance and
Chapter 7 of the Climate Leaders Design
Principles provides general guidelines
for implementing a QA/QC process for
all emission estimates. For MSW landfill
sources, a review of input data and emission
factors should be verified for various
approaches, specifically if customized defaults
were developed based on site specific data.
QA/QC may include, but not limited to:
• Landfill methane emissions calculated using
Landfill Gas Emission Model compared with
emissions calculated using proprietary gas
generation models developed by industry
experts or other agencies.
• Landfill methane emissions calculated by
gas collection system efficiency in compari-
son to emissions estimated through gas
modeling.
Examining the quality assurance and quality
control program associated with equipment
used for facility level LFG flow rate and
composition measurements and any equip-
ment used to calculate site-specific
emissions factors, or emissions.
Performing back-checks and re-calculations
for all equations used.
Landfill gas sampling and third-party labora-
tory analysis using the applicable U.S. EPA
test methods for determination of methane
and total hydrocarbon content.
Ensuring that measuring and monitoring
equipment is maintained, operated and
calibrated based on manufacturer's recom-
mendation and calibration and maintenance
records kept for audit purposes.
CLIMATE LEADERS GHG INVENTORY PROTOCOL
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M S W Landfill Sources — Guidance
LandGEM Sample Output
The following is a sample text emission output report generated using LandGEM Version 2.01
and based on the example and model input parameters in Section 2.1.
LandGEM 2.01 Text Report
Source: Operating Parameters: ALANDFILLOOO
Model Parameters
Lo : 100.00 mA3/Mg ***** User Mode Selection *****
k : 0.0200 1/yr ***** User Mode Selection *****
NMOC : 4000.00 ppmv ***** User Mode Selection *****
Methane : 50.0000 % volume
Carbon Dioxide : 50.0000 % volume
Landfill
Parameters
Landfill type : No Co-Disposal
Year Opened : 1982 Current Year : 2003 Closure Year: 2012
Capacity : 2400000 Mg
Average Acceptance Rate Required from Current Year to Closure Year : 80000.00 Mg/year
Model Results
Year
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
Refuse In
Place (Mg)
8.000E+04
1.600E+05
2.400E+05
3.200E+05
4.000E+05
4.800E+05
5.600E+05
6.400E+05
7.200E+05
8.000E+05
8.800E+05
Methane Emission Rate
(Mg/yr)
1.067E+02
2.114E+02
3.139E+02
4.145E+02
5.130E+02
6.096E+02
7.043E+02
7.971E+02
8.880E+02
9.772E+02
1.065E+03
(Cubic m/yr)
1.600E+05
3.168E+05
4.706E+05
6.212E+05
7.689E+05
9.137E+05
1.056E+06
1.195E+06
1.331E+06
1.465E+06
1.596E+06
Methane Emission Rate
Year
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Refuse In
Place (Mg)
9.600E+05
1.040E+06
1.120E+06
1.200E+06
1.280E+06
1.360E+06
1.440E+06
1.520E+06
1.600E+06
1.680E+06
(Mg/yr)
1.150E+03
1.234E+03
1.317E+03
1.397E+03
1.476E+03
1.554E+03
1.630E+03
1.704E+03
1.777E+03
1.849E+03
(Cubic m/yr)
1.724E+06
1.850E+06
1.973E+06
2.094E+06
2.213E+06
2.329E+06
2.443E+06
2.554E+06
2.664E+06
2.771E+06
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&EPA
United States
Environmental Protection
Agency
Office of Air and Radiation (6202J)
EPA430-K-04-011
October 2004
www.epa.gov/climateleaders
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