User's Manual
Central America Landfill Gas Model
Version 1.0
Prepared on behalf of:
LANDFILL METHANE
OUTREACH PROGRAM
Victoria Ludwig
U.S. Environmental Protection Agency
Washington, DC
Prepared by:
G. Alex Stege
SCS Engineers
Phoenix, AZ 85008
EPA Contract 68-W-00-110
Task Order 11
Dana L. Murray, PE
Project Manager
SCS Engineers
Reston, VA 20190
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DISCLAIMER
This user's guide has been prepared specifically for Central America on behalf of the
U.S. EPA's Landfill Methane Outreach Program, U.S. Environmental Protection Agency and
U.S. Agency for International Development. The methods contained within are based on
engineering judgment and represent the standard of care that would be exercised by a
professional experienced in the field of landfill gas projections. The U.S. EPA and SCS
Engineers do not guarantee the quantity of available landfill gas, and no other warranty is
expressed or implied. No other party is intended as a beneficiary of this work product, its
content, or information embedded therein. Third parties use this report at their own risk. The
U.S. EPA and SCS Engineers assume no responsibility for the accuracy of information obtained
from, compiled, or provided by other parties.
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ABSTRACT
This document is a user's guide for a computer model, Version 1.0 of a landfill gas
generation model for estimating landfill gas generation and recovery from municipal solid waste
landfills in Central America (Central America LFG Model). The model was developed by SCS
Engineers under contract to the U.S. EPA's Landfill Methane Outreach Program (LMOP). The
Central America LFG Model can be used to estimate landfill gas generation rates from landfills,
and potential landfill gas recovery rates for landfills that have, or plan to have, gas collection and
control systems in Central America.
The Central America LFG Model is an Excel® spreadsheet model based on a first order
decay equation. The model requires the user to input site-specific data for landfill opening and
closing years, refuse disposal rates, average annual precipitation, and collection efficiency. The
model provides default values for waste composition and input variables (k and L0) for each
country. The default values were developed using data on climate, waste characteristics, and
disposal practices in Central America, and the estimated effect of these conditions on the
amounts and rates of LFG generation. Actual LFG recovery rates from two landfills in Central
America were evaluated, but insufficient data were available for model calibration. A guide to
evaluate a site's collection efficiency, which is used by the model to derive LFG recovery
estimates from model projections of LFG generation, is also provided.
The Central America LFG Model was developed with the goal of providing accurate and
conservative projections of LFG generation and recovery. Other models evaluated during the
model development process included the Mexico LFG Model, Clean Development Mechanism
(CDM) Method AM0025 v.3.(March 2006), and the Intergovernmental Panel on Climate Change
(IPCC) 2006 Waste Model. The Central America LFG Model incorporates components of each
of these models that help it to reflect conditions at disposal sites in Central America. A
comparison of model results shows that the Central America Model typically provides estimates
of LFG generation that are approximately mid-way between the CDM Method and IPCC Model
results.
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TABLE OF CONTENTS
Section	Page
Disclaimer	i
Abstract	ii
List of Figures	iii
List of Tables	iv
Glossary of Terms	v
1.0 Introduction	1-1
1.1	Landfill Gas Generation	1-2
1.1.1	Methane Generation Rate Constant (k)	1-3
1.1.2	Potential Methane Generations Capacity (L0)	1-5
1.2	Landfill Gas Recovery	1-7
1.3	The Model	1-7
2.0 Estimating Landfill Gas Generation and Recovery	2-1
2.1	Model Inputs	2-1
2.1.1. Estimating Collection Efficiency	2-5
2.2	Model Outputs / Table	2-7
2.3	Model Outputs / Graph 	2-10
3.0 References	3-1
Figures
1	Model Inputs	2-2
2	Model Inputs (continued)	2-4
3	Sample Model Output / Table	2-9
4	Sample Model Output / Graph	2-11
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Tables
1	Methane Generation Rate Constant (k) - Wet Climate	1-4
(Rainfall >= 1000 mm/year)
2	Methane Generation Rate Constant (k) - Moderate Climate	1-4
(Rainfall > = 750-999 mm/year)
3	Methane Generation Rate Constant (k) - Dry Climate	1-5
(Rainfall >= 500-749 mm/year)
4	Potential Methane Generation Capacity (L0)	1-6
5	Methane Correction Factor (MCF)	1-6
6	Landfill Collection Efficiency	2-6
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GLOSSARY OF TERMS
Term
Definition
Collection Efficiency
The estimated percentage of generated landfill
gas which is or can be collected in a gas
collection system.
Collection System Coverage
The estimated percentage of a landfill's refuse
mass that is potentially within the influence of a
gas collection system's extraction wells.
Collection system coverage describes the
fraction of recoverable gas that can be captured
and can reach 100% in a comprehensive
collection system (unlike collection efficiency
which is always less than 100%).
Design Capacity of the Landfill
The total amount of refuse that can be disposed
of in the landfill.
Landfill Gas
Landfill gas is a product of biodegradation of
refuse in landfills and consists of primarily
methane and carbon dioxide, with trace amounts
of non-methane organic compounds and air
pollutants.
Methane Generation Rate Constant
(k)
k is a model constant that determines the
estimated rate of landfill gas generation. The
first-order decomposition model assumes that k
values before and after peak landfill gas
generation are the same, k is a function of
moisture content in the landfill refuse,
availability of nutrients for methanogens, pH,
and temperature. (Units = 1/year)
Potential Methane Generation
Capacity (L0)
L0 is a model constant that represents the
potential capacity of a landfill to generate
methane (a primary constituent of landfill gas).
L0 depends on the amount of cellulose in the
refuse. (Units = m3/Mg)
Closure Year
The year in which the landfill ceases, or is
expected to cease, accepting waste.
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1.0: INTRODUCTION
The Central America Landfill Gas Model (Central America LFG Model) provides an
automated estimation tool for quantifying landfill gas generation and recovery from municipal
solid waste (MSW) landfills in Belize, Costa Rica, El Salvador, Guatemala, Honduras,
Nicaragua, and Panama. This manual provides an introduction to the model and step-by-step
instructions for using the model.
The main purpose of the Central America LFG Model is to provide landfill owners and
operators with a tool to use to evaluate the feasibility and potential benefits of collecting and
using the generated landfill gas for energy recovery or other uses. To accomplish this purpose,
this computer model provides estimates of potential landfill gas recovery rates. This is
accomplished using the landfill gas generation rates estimated by the model and estimates of the
efficiency of the collection system in capturing generated gas, known as the collection
efficiency. The model provides landfill gas recovery estimates by multiplying the landfill gas
generation by the estimated recovery efficiency.
Landfill gas is generated by the decomposition of refuse in the landfill, and can be
recovered through the operation of gas collection facilities installed at the landfill. The following
information is needed to estimate landfill gas generation and recovery from a landfill (see the
Glossary of Terms):
•	The design capacity of the landfill;
•	The amount of refuse in place in the landfill, or the annual refuse acceptance rate for the
landfill;
•	The methane generation rate (k) constant;
•	The potential methane generation capacity (L0);
•	The collection efficiency of the gas collection system; and
•	The years the landfill has been and will be in operation.
The model employs a first-order exponential decay function that assumes that LFG
generation is at its peak following a time lag representing the period prior to methane generation.
The model assumes a six month time lag between placement of waste and LFG generation. For
each unit of waste, after six months the model assumes that LFG generation decreases
exponentially as the organic fraction of waste is consumed.
For sites with known (or estimated) year-to-year solid waste acceptance rates, the model
estimates the LFG generation rate in a given year using the following equation, which is used by
the U.S. EPA's Landfill Gas Emissions Model (LandGEM) version 3.02 (EPA, 2005).
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n 1
QM = ZZ2kL0 (Mj/10) (e"k,ij)
1=1 j=0.1
Qm -
maximum expected LFG generation flow rate (m3/yr);
i =
1 year time increment
n =
(year of the calculation) - (initial year of waste acceptance)
j =
0.1 year time increment
k =
methane generation rate (1/yr);
L0 =
potential methane generation capacity (m3/Mg);
M; =
mass of solid waste disposed in the ith year (Mg);
tij =
age of the jth section of waste mass disposed in the ith year (decimal years).
The above equation is used to estimate LFG generation for a given year from cumulative
waste disposed up through that year. Multi-year projections are developed by varying the
projection year, and then re-applying the equations. The year of maximum LFG generation
normally occurs in the closure year or the year following closure (depending on the disposal rate
in the final years).
The Central America LFG Model requires site-specific data for all the information
needed to produce generation estimates, except for the k and L0 values. The model provides
default values for k and L0. The default values are based on climate and waste composition data
gathered from representative landfills and cities in Central America. The default k and L0 values
vary depending on country, waste composition, and average annual precipitation, and can be
used to produce typical landfill gas generation estimates for landfills located in each of the seven
countries in Central America.
EPA recognizes that modeling landfill gas generation and recovery accurately is difficult
due to limitations in available information for inputs to the model. However, as new landfills are
constructed and operated, and better information is collected, the present modeling approach can
be improved. In addition, as more landfills in Central America develop gas collection and control
systems, additional data on landfill gas generation and recovery will become available for model
calibration and the development of improved model default values.
Questions and comments concerning the landfill gas model should be directed to Victoria
Ludwig of EPA's LMOP at (202) 343-9291, or by e-mail at Ludwig.Victoria@epamail.epa.gov.
1.1 Landfill Gas Generation
The Central America LFG Model estimates landfill gas generation resulting from the
biodegradation of refuse in landfills. The anaerobic decomposition of refuse in solid waste
landfills generates landfill gas. The composition of MSW landfill gas is assumed by the model to
be about 50 percent methane (CH4) and 50 percent other gases, including carbon dioxide (C02)
and trace amounts of other compounds.
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This computer model uses a first-order decomposition rate equation and estimates
volumes of landfill gas generation in cubic meters per hour (m3/hr) and cubic feet per minute
(cfm). It also estimates the energy content of generated landfill gas in million British Thermal
Units per hour (mmBtu/hr), and the maximum power plant capacity that could be fueled by the
collected landfill gas (MW). Total landfill gas generation is estimated by doubling methane
generation (the landfill gas is assumed to be half methane and half carbon dioxide). Methane
generation is estimated using two parameters: (1) L0 is the potential methane generation capacity
of the refuse, and (2) k is the methane generation rate. Landfill gas generation is assumed to be at
its peak upon closure of the landfill or final placement of waste at the site. Although the model
allows the user to enter L0 and k values derived using site-specific data collected at the landfill, it
is recommended that the provided default values be used for most modeling applications. 1
1.1.1 Methane Generation Rate Constant (k)
The methane generation rate constant, k, determines the rate of generation of methane
from refuse in the landfill. The units for k are in year-1, and describes the rate at which refuse
placed in a landfill decays and produces biogas. The higher the value of k, the faster total
methane generation at a landfill increases (as long as the landfill is still receiving waste) and then
declines (after the landfill closes) over time. The value of k is a function of the following factors:
(1) refuse moisture content, (2) availability of nutrients for methane-generating bacteria, (3) pH,
and (4) temperature.
Different waste types can have significantly different k values as a result of differences in
decay rates. Food waste, for example decays faster than paper or wood. The Central America
LFG Model assigns two different categories of k values to organic waste materials depending on
whether they decay rapidly or slowly. Fast-decay waste materials include food waste and
selected garden and park waste ("green waste"). Slow-decay waste materials include all other
organic materials, including the remaining portion of garden and park waste, paper, textiles,
rubber, leather, and bones. Because individual materials in each category also will differ, the
ratio between the fast-decay waste k value and the slow-decay waste k value varies depending on
waste composition.
The k values also vary with climate, especially precipitation. Because most of Central
America experiences high rainfall, most landfills experience moisture conditions that tend to
maximize waste decay rates and k values. The Central America LFG Model assumes no
differences in k values for sites experiencing 1,000 mm per year or more precipitation. For the
few areas that receive less than 1,000 mm per year precipitation, the model assigns lower k
values appropriate for the local climate.
Unless user-specified k values, or user-specified waste composition data, are entered into
the Central America LFG Model, default values are used for k. For each of the seven countries
1 Site-specific L0 and k values may be developed for landfills with operating gas collection and
control systems by calibrating the Central America LFG Model using known landfill gas
recovery data.
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default k values have been calculated, including a fast-decay k and a slow-decay k. The fast
decay k values are the same for all seven countries, and are set at 0.23 per year, the value used
by CDM Method AM0025 (UNFCCC, 2006). The slow decay k values vary depending on waste
composition. The model also adjusts the k values downward for sites experiencing less than
1,000 mm per year precipitation. Tables 1 through 3 provide the default k values used by the
program, depending on the amount of precipitation experienced at the landfill:
TABLE 1: METHANE GENERATION RATE (k)
WET CLIMATE (Rainfall >= 1,000 mm/year)
Country
Fast k
(per yc^r)
Slow k
(per year)
Belize
0.23
0.033
Costa Rica
0.23
0.028
El Salvador
0.23
0.027
Guatemala
0.23
0.030
Honduras
0.23
0.030
Nicaragua
0.23
0.025
Panama
0.23
0.029
TABLE 2: METHANE GENERATION RATE (k)
MODERATE CLIMATE (Rainfall = 750-999 mm/year)
Country
Fast k
(per yc^r)
Slow k
(per year)
Belize
0.20
0.029
Costa Rica
0.20
0.024
El Salvador
0.20
0.023
Guatemala
0.20
0.026
Honduras
0.20
0.026
Nicaragua
0.20
0.022
Panama
0.20
0.025
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TABLE 3: METHANE GENERATION RATE (k)
DRY CLIMATE (Rainfall = 500-749 mm/year)
Country
Fast k
(per yc^r)
Slow k
(per year)
Belize
0.18
0.026
Costa Rica
0.18
0.022
El Salvador
0.18
0.021
Guatemala
0.18
0.024
Honduras
0.18
0.023
Nicaragua
0.18
0.020
Panama
0.18
0.022
1.1.2 Potential Methane Generation Capacity (L0)
Except in dry climates where a lack of moisture limits methane generation, the value for
the potential methane generation capacity of refuse (L0) depends almost exclusively on the type
of refuse present in the landfill. The higher the cellulose content of the refuse, the higher the
value of L0. The units of L0 are in cubic meters per tonne of refuse, which means that the L0
value describes the total amount of methane gas potentially produced by a tonne of refuse as it
decays. The values of theoretical and obtainable L0 range from 6.2 to 270 m3/Mg refuse (EPA,
1991). Unless a user-specified L0 value is entered into the Central America LFG Model, default
values are used for L0. The model uses waste composition data to calculate default L0 values for
each country, including a total waste L0, a fast decay organic waste L0, and a slow-decay organic
waste L0. The default L0 values shown in Table 4 are used by the model for each of the seven
countries.
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TABLE 4: POTENTIAL METHANE GENERATION CAPACITY (L0)

Total
Fast-decay
Slow-decay
Country
Waste L0
Waste L0
Waste L0
(m3/Mg)
(m3/Mg)
(m3/Mg)
Belize
78
71
199
Costa Rica
96
70
200
El Salvador
91
68
189
Guatemala
89
71
198
Honduras
70
68
209
Nicaragua
82
72
183
Panama
101
68
207
1.1.2.1 Methane Correction Factor
The Methane Correction Factor (MCF) is a final adjustment to model estimates of LFG
generation that accounts for the degree to which wastes will decay anaerobically. The MCF
varies depending on waste depth and landfill type, as defined by site management practices. At
managed, sanitary landfills, it is assumed that all waste decay will be anaerobic (MCF of 1). At
landfills or dumps with conditions less conducive to anaerobic decay, the MCF will be lower to
reflect the extent of aerobic conditions at these sites. Table 5 summarizes the recommended
MCF adjustments.
TABLE 5: METHANE CORRECTION FACTOR (MCF)
Site Management
Depth <5m
Depth >=5m
Unmanaged Disposal Site
0.4
0.8
Managed Landfill
0.8
1.0
Semi-Aerobic Landfill
0.3
0.5
Unknown
0.4
0.8
Waste depth of at least five meters promotes anaerobic decay; at shallower sites, waste
decay may be primarily aerobic. A managed landfill is defined as having controlled placement of
waste (waste directed to specific disposal areas, a degree of control of scavenging and fires), and
one or more of the following: cover material, mechanical compacting, or leveling of waste
(IPCC, 2006). A semi-aerobic landfill has controlled placement of waste and all of the following
structures for introducing air into the waste layer: permeable cover material, leachate drainage
system, regulating pondage, and gas ventilation system (IPCC, 2006).
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1.2	Landfill Gas Recovery
Landfill gas generated in landfills can be captured by gas collection and control systems
that typically burn the gas in flares. Alternatively, the collected gas can be used beneficially.
Beneficial uses of landfill gas include use as fuel in energy recovery facilities, such as internal
combustion engines, gas turbines, microturbines, steam boilers, or other facilities that use the gas
for electricity generation.
In addition to the energy benefits from the beneficial use of landfill gas, collection and
control of generated landfill gas helps to reduce landfill gas emissions that are harmful to the
environment. The U.S. EPA has determined that landfill gas emissions from MSW landfills
cause, or contribute significantly to, air pollution that may reasonably be anticipated to endanger
public health or welfare. Some are known or suspected carcinogens, or cause other non-
cancerous health effects. Public welfare concerns include the odor nuisance from the landfill gas
and the potential for methane migration, both on-site and off-site, which may lead to explosions
or fires. The methane emitted from landfills is also a concern because it is a greenhouse gas
thereby contributing to the challenge of global climate change.
The main purpose of the Central America LFG Model is to provide landfill owners and
operators in Central America with a tool to use to evaluate the feasibility and potential benefits
of collecting and using the generated landfill gas for energy recovery or other uses. To fulfill this
purpose, the model provides estimates of potential landfill gas recovery rates. This is
accomplished using the landfill gas generation rates estimated by the model and estimates of the
efficiency of the collection system in capturing generated gas, known as the collection
efficiency. The model provides landfill gas recovery estimates by multiplying the landfill gas
generation by the estimated collection efficiency.
1.3	The Model
The Central America LFG Model can be operated in a Windows 98®, Windows 2000®,
Windows XP®, or Vista environment. The program is a Microsoft Excel® spreadsheet, which
allows the user considerable control over model calculations and output appearances. Open the
model file ("LMOP Central America Model.xls") by choosing "file" "open," and then "open"
when the correct file is highlighted. The model has seven worksheets that are accessible by
clicking on the tabs at the bottom of the Excel® window screen. The seven worksheets are as
follows:
•	A model inputs worksheet;
•	A waste composition worksheet;
•	A model outputs worksheet in a table format;
•	A model outputs worksheet in a graph format; and
•	Three model calculations worksheets ("amounts," "calcsl," and "calcs2").
When using the model, most of the editing by the user takes place in the model inputs
worksheet. Some editing may be required in the outputs worksheet for formatting purposes.
Also, selected cells in the waste composition worksheet allow the user to input site-specific
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waste composition data. The remaining cells in the waste composition worksheet and all
calculation worksheets should not be changed and are password-protected to prevent changes.
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2.0 ESTIMATING LANDFILL GAS GENERATION AND RECOVERY
2.1 Model Inputs
All model inputs except for site-specific waste composition data are to be entered into the
"Inputs" worksheet. Cells with red bold text require user inputs. See Figure 1 for model inputs.
Cells highlighted in yellow should not be changed. The following inputs are required to run the
model properly and produce acceptable outputs (tables and graphs):
Step 1: Enter the name and location of the landfill (Cell A4 ). The information entered
here will automatically appear in the heading of the output table.
Step 2: Select the name of the country in which the landfill is located (Cell B5). The
country selected here will be used by the model to look up waste composition data.
Step 3: Select either a "Yes" to indicate that there is site-specific waste composition data
available to use in the model or a "No" for the model to run with the country-specific
default waste composition figures (Cell B6). If a "Yes" is entered here, the model will
run with waste composition figures entered into the Waste Composition worksheet by the
user. Enter site specific waste composition data into Cells B4 through BIO and B14
through B17 of the waste composition worksheet. You will be prompted to enter a
password to unlock the cells for editing. Enter "lmop" (all lowercase letters).
Step 4: Enter the year the landfill opened and began receiving waste (Cell B7). This
value will feed into the table of numbers below and in the output table.
Step 5: The estimated annual growth in disposal rates (goes into Cell B8 - see Figure 1).
The rate entered will feed into the table of numbers below and in the output table.
Step 6: The average annual precipitation in mm per year at the landfill (goes into Cell B9
- see Figure 1). This information can be obtained by looking up precipitation data for the
closest city or town at www.worldclimate.com. This value will be used to adjust default
values for k if the site experiences less than 1,000 mm per year of precipitation.
Step 7: Enter the average landfill depth in areas filled with waste (Cell BIO). This value
will be used to calculate the Methane Correction Factor.
Step 8: Enter the number which designates the landfill type, as defined by site design and
management practices (Cell B11). Instructions in Cell CI 1 list the numbers to use for
designating site type (see Table 5 and page 1-7 above for details). The information
entered here will be used to calculate the Methane Correction Factor.
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FIGURE 1. MODEL INPUTS

A
B
C
1
LMOP CENTRAL AMERICA BIOGAS MODEL v.l March 2007

2
Developed by SCS Engineers, LMOP contractor

3
PROJECTION OF BIOGAS GENERATION AND RECOVERY

4
LANDFILL, , El SALVADOR

5
Country:
3

6
Site-Specific Waste Composition Data?
N

7
Year Opened:
1978

8
Estimated Growth in Annual Disposal:
2.0%

9
Average annual precipitation:
1,200
mni/yr
10
Average Landfill Depth:
20.0
m
11
Site Design and Management Practices:
2

12
Methane Content of Landfill Biogas Adjusted to:
50%

13
Methane Correction Factor (MCF):
1.0

14
Fast-decay Organic Waste Methane Generation Rate (k):
0.23
1/yr
15
Slow-decay Organic Waste Methane Generation Rate (k):
0.027
1/yr
16
Potential Methane Generation Capacity (L0):
91.0
m3/Mg
17
Fast-decay Organic Waste L0:
67.6
mJ/Mg
18
Slow-decay Organic Waste L0:
189.0
rnVMg
Step 9: Enter the amount of wastes disposed (in metric tonnes) for each year the site is
open (Cells B25 - B125 ). See Figure 2. The disposal estimates should be based on
available records of actual disposal rates and be consistent with site-specific data on
amount of waste in place, total site capacity, and projected closure year. If the landfill has
a history of significant fires, an estimated amount or percentage of waste combusted
should be subtracted from the annual disposal inputs.
•	Enter in the annual disposal rates for years with recorded data.
•	For years without historical data, adjust the opening year disposal amount until the
calculated total tonnes in place matches estimated actual tonnes in place (as of the
most recent year with waste in place data). The estimated annual growth rate (user
input in Cell B8) is used to fill in disposal figures for years without data.
•	The model uses the estimated growth rate to calculate future waste disposal rates
unless the user enters values in cells that provide future disposal inputs. Future
disposal estimates should be adjusted to be consistent with estimates of remaining
site capacity and closure year.
•	Enter a "0" into the cell corresponding to the year following site closure. The model
accommodates up to 101 years of waste disposal history.
Step 10: Enter the estimated collection efficiency for each year after a gas collection
system was/will be installed (Cells D25 - D125). See Figure 2.
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•	The input sheet currently has 0% collection efficiency for the first 30 years of site
operation and 60% for the remaining years.
•	Collection system efficiency for years prior to the present should reflect the status of
the collection system in prior years.
•	Collection system efficiency for future years should reflect the estimated collection
system build-out in future years.
•	Additional instruction on how to estimate collection efficiency is provided in
Subsection 2.1.1.
Step 11: Enter the actual landfill gas recovery rates in cubic meters per hour (for sites
with active gas collection systems) into Cells E25 - E125 (see Figure 2). This should be
the average annual total landfill gas flow at the flare station and/or energy recovery plant
(NOT the sum of flows at individual wells). Adjust all flow rates to 50% methane
equivalent by multiplying the measured flow by the measured methane content of the
landfill gas and then dividing the result by 50%. The numbers placed in these cells will be
displayed in the graph output sheet, so do not input zeros for years with no flow data
(leave blank).
Equation for adjusting methane content to 50%:
Measured x Measured methane %
Flow Rate	50 % methane
Flow rate
at 50% methane
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FIGURE 2. MODEL INPUTS (Continued)
23
A
B
c
D
E
24
Year
Metric
Cumulative
Collection
Actual
Tonnes
Metric
System
Recovery
Disposed
Tonnes
Efficiency
(m3/hr)
25
1978
175,000
175.000
0%

26
1979
179,000
354.000
0%

27
1980
183,000
537.000
0%

28
1981
187,000
724.000
0%

29
1982
191,000
915.000
0%

30
1983
195,000
1.110.000
0%

31
1984
199,000
1.309.000
0%

32
1985
203,000
1.512.000
0%

33
1986
207,000
1.719.000
0%

34
1987
211,000
1.930.000
0%

35
1988
215,000
2.145.000
0%

36
1989
219,000
2.364.000
0%

37
1990
223,000
2.587.000
0%

38
1991
227,000
2.814.000
0%

39
1992
232,000
3.046.000
0%

40
1993
237,000
3.283.000
0%

41
1994
242,000
3.525.000
0%

42
1995
247,000
3.772.000
0%

43
1996
252,000
4.024.000
0%

44
1997
257,000
4.281.000
0%

45
1998
262,000
4.543.000
0%

46
1999
267,000
4.810.000
0%

47
2000
272,000
5.082.000
0%

48
2001
277,000
5.359.000
0%

49
2002
283,000
5.642.000
0%

50
2003
289,000
5.931.000
0%

51
2004
295,000
6.226.000
0%

52
2005
301,000
6.527.000
0%

53
2006
307,000
6.834.000
0%

54
2007
313,000
7.147.000
0%

55
2008
0
7.147.000
60%
2,500
56
2009
0
7.147.000
60%

57
2010
0
7.147.000
60%

58
2011
0
7.147.000
60%

59
2012
0
7.147.000
60%

60
2013
0
7.147.000
60%

61
2014
0
7.147.000
60%

62
2015
0
7.147.000
60%

63
2016
0
7.147.000
60%

64
2017
0
7.147.000
60%

65
2018
0
7.147.000
60%

66
2019
0
7.147.000
60%

67
2020
0
7.147.000
60%

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2.1.1 Estimating Collection Efficiency
Collection efficiency is a measure of the ability of the gas collection system to capture
generated landfill gas. It is a percentage value that is applied to the landfill gas generation
projection produced by the model to estimate the amount of landfill gas that is or can be captured
for flaring or beneficial use. Although rates of landfill gas capture can be measured, rates of
generation in a landfill cannot be measured (hence the need for a model to estimate generation);
therefore there is considerable uncertainty regarding actual collection efficiencies achieved at
landfills.
In response to the uncertainty regarding collection efficiencies, the U.S. EPA (EPA,
1998) has published what it believes are reasonable collection efficiencies for landfills in the
U.S. that meet U.S. design standards and have "comprehensive" gas collection systems.
According to the EPA, collection efficiencies at such landfills typically range from 60% to 85%,
with an average of 75%. A comprehensive landfill gas collection system is defined as a system
of vertical wells and/or horizontal collectors providing 100 percent collection system coverage of
all areas with waste within one year after the waste is deposited. Most landfills, particularly
those that are still receiving wastes, will have less than 100 percent collection system coverage,
and will require a "coverage factor" adjustment to the estimated collection efficiency. Sites with
security issues or large numbers of uncontrolled waste pickers will not be able to install
equipment in unsecured areas and cannot achieve comprehensive collection system coverage.
Table 6, "Landfill Collection Efficiency," shows an example of how to estimate the
collection efficiency using the landfill characteristics listed and deducting percentages for
landfills without these characteristics. For example, if a landfill has all the characteristics listed
in Table 6, then the estimated efficiency is 85% times the coverage factor.
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TABLE 6: LANDFILL COLLECTION EFFICIENCY
Item
No.
Landfill Characteristics
Collection Efficiency Discount
Site meets some
criteria
Site meets none
of the criteria
1
Managed placement of waste, waste
compaction, and grading
8%
15%
2
Waste depths at least 8 m, preferably > 15m
5%
10%
3
Soil cover applied over newly deposited
refuse at least weekly, preferably on a daily
basis. Closed sites should have a final soil
cover installed within a few years of closure.
5%
10%
4
A composite bottom liner consisting of
synthetic (plastic) layer over 2 feet (0.6
meter) of clay or similar material.
2%
5%
5
A comprehensive landfill gas collection
system with vertical wells and/or horizontal
collectors providing 100% collection system
coverage of all areas with waste within one
year after the waste is deposited.
% of filled area without wells
6
A gas collection system which is operating
effectively so that all wells are fully
functioning (i.e., relatively free of liquids
and drawing landfill gas under vacuum).
% wells not fully functioning or filled
with leachate
Note that the recommended method for estimating collection efficiency assumes that
some portion (at least 15%) of generated landfill gas will escape collection, no matter how well
designed the landfill or how comprehensive the gas collection system is. The following steps are
recommended to adjust the efficiency below 85%:
•	To evaluate collection efficiency, start at 85%, and then apply a discount to the
extent the site does not meet the criteria of landfill characteristics, as described in
Table 6 and below.
•	We suggest up to a 15% discount for not meeting item number 1, up to a 10%
discount each for not meeting items 2 and 3, and up to a 5% discount for not
meeting item number 4 (i.e., a 40% discount to collection efficiency if the landfill
does not, even in part, meet any of the first four criteria).
•	To account for item number 5, the resulting discounted estimate should then be
multiplied by the existing or forecasted collection system coverage of the refuse
mass (see glossary for a definition of collection system coverage). Tips to
consider when evaluating collection system coverage are provided below.
•	The final discount to collection efficiency (item 6 above) involves an evaluation
of collection system operations to determine the percentage of operational wells.
This evaluation should consider the effect of high leachate levels on limiting LFG
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extraction. The determination of whether or not a well is operational should be
based on available wellfield monitoring data, including wellhead pressure (all
wells should be under vacuum), well methane content, and well oxygen contents
(low methane percentages under 40% and high oxygen percentages over 5%
indicate that air instead of landfill gas is being drawn into the well). After
accounting for the importance of the non-functioning wells (see below), multiply
the percentage of operational wells by the value calculated in the above steps to
develop a collection efficiency estimate.
• The importance of a non-functioning well should be taken into account when
estimating the percentage of non-functioning wells. For example, a site with a
non-functioning well in the vicinity of other wells that are functional should cause
less of a collection efficiency discount than a site with a non-functioning well that
is the only well in the area available to draw landfill gas from a significant portion
of the site.
Evaluation of collection system coverage requires a fair degree of familiarity with the
system design. Well spacing and depth are important factors. The following describes the various
scenarios to consider:
•	Deeper wells can draw landfill gas from a larger volume of refuse than shallow wells
because greater vacuum can be applied to the wells without drawing in air from the
surface.
•	Landfills with deep wells (greater than about 20 meters) can effectively collect landfill
gas from all areas of the site with vertical well densities as low as two wells or less per
hectare.
•	Landfills with shallower wells will require greater well densities, perhaps more than 2
wells per hectare, to achieve the same coverage.
•	Although landfills with a dense network of wells will collect more total gas than landfills
with more widely spaced wells, landfills with a small number of well-spaced wells
typically collect more gas per well (due to their ability to influence a larger volume of
refuse per well) than wells at landfills with a dense network of wells.
2.2 Model Outputs - Table
Model results are displayed in a table located in the "Outputs-Table" worksheet that is ready for
printing with minimal editing (see Figure 3 for a sample table layout). The title of the table has
been set by user inputs in the Inputs worksheet. The table provides the following information
which was either copied from the Inputs worksheet or calculated by the model:
•	Projection years starting with the landfill opening year and ending in a year of the user's
choosing.
•	Annual disposal rates.
•	Cumulative amount of waste in place for each projection year.
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•	Landfill gas generation rates for each projection year in cubic meters per hour, cubic feet
per minute, and million British Thermal Units (mmBtu) per hour.
•	Collection system efficiency for each projection year.
•	Landfill gas recovery rates for each projection year in cubic meters per hour, cubic feet
per minute, and mmBtus per hour.
•	The maximum power plant capacity that could be supported by this flow in MW.
•	The estimated baseline landfill gas recovery rate in cubic meters per hour.
•	The estimated methane emission reductions in tonnes CH4/year and in tonnes C02e/year
•	The methane content assumed for the model projection (50% in most cases).
•	The k values used for the model run.
•	The L0 values used for the model run.
The table is set up to display up to 100 years of landfill gas generation and recovery estimates.
As provided, the table shows 53 years of information. The last 47 years are in hidden rows. The
user will likely want to change the number of years of information displayed, depending on how
old the site is and how many years into the future the user wants to display information.
Typically, projections up to the year 2030 are adequate for most uses of the model. To hide
additional rows, highlight cells in the rows to be hidden and select "Format" "Row" "Hide". To
unhide rows, highlight cells in rows above and below rows to be displayed, and select "Format"
"Row" "Unhide".
To print the table, select "File" "Print" "OK". The table should print out correctly formatted.
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Central America LFG Model Users Manual	March 29, 2007
FIGURE 3. SAMPLE MODEL OUTPUT TABLE
TABLE 1
PROJECTION OF BIOGAS GENERATION AND RECOVERY
	LANDFILL,	, El SALVADOR
Year
Disposal
Rate
Refuse
In-Place
LFG
Generation
Collection
System
Efficiency
Predicted LFG
Recovery
Maximum
Power Plant
Capacity*
Methane Emissions
Reduction Estimates**
(Mg/yr)
(Mg)
(m3/hr)
(cfm)
(mmBtu/hr)
(%)
(m3/hr)
(cfm)
(mmBtu/hr)
(MW)
(tonnes
CH4/yr)
(tonnes
C02eq/yr)
1978
175,000
175,000
0
0
0.0
0%
0
0
0.0
0.0
0
0
1979
179,000
354,000
380
224
6.8
0%
0
0
0.0
0.0
0
0
1980
183,000
537,000
701
413
12.5
0%
0
0
0.0
0.0
0
0
1981
187,000
724,000
975
574
17.4
0%
0
0
0.0
0.0
0
0
1982
191,000
915,000
1,211
713
21.6
0%
0
0
0.0
0.0
0
0
1983
195,000
1,110,000
1,417
834
25.3
0%
0
0
0.0
0.0
0
0
1984
199,000
1,309,000
1,599
941
28.6
0%
0
0
0.0
0.0
0
0
1985
203,000
1,512,000
1,762
1,037
31.5
0%
0
0
0.0
0.0
0
0
1986
207,000
1,719,000
1,910
1,124
34.1
0%
0
0
0.0
0.0
0
0
1987
211,000
1,930,000
2,046
1,204
36.6
0%
0
0
0.0
0.0
0
0
1988
215,000
2,145,000
2,172
1,279
38.8
0%
0
0
0.0
0.0
0
0
1989
219,000
2,364,000
2,291
1,348
40.9
0%
0
0
0.0
0.0
0
0
1990
223,000
2,587,000
2,404
1,415
43.0
0%
0
0
0.0
0.0
0
0
1991
227,000
2,814,000
2,511
1,478
44.9
0%
0
0
0.0
0.0
0
0
1992
232,000
3,046,000
2,615
1,539
46.7
0%
0
0
0.0
0.0
0
0
1993
237,000
3,283,000
2,718
1,600
48.6
0%
0
0
0.0
0.0
0
0
1994
242,000
3,525,000
2,820
1,660
50.4
0%
0
0
0.0
0.0
0
0
1995
247,000
3,772,000
2,922
1,720
52.2
0%
0
0
0.0
0.0
0
0
1996
252,000
4,024,000
3,023
1,779
54.0
0%
0
0
0.0
0.0
0
0
1997
257,000
4,281,000
3,124
1,839
55.8
0%
0
0
0.0
0.0
0
0
1998
262,000
4,543,000
3,224
1,898
57.6
0%
0
0
0.0
0.0
0
0
1999
267,000
4,810,000
3,325
1,957
59.4
0%
0
0
0.0
0.0
0
0
2000
272,000
5,082,000
3,425
2,016
61.2
0%
0
0
0.0
0.0
0
0
2001
277,000
5,359,000
3,526
2,075
63.0
0%
0
0
0.0
0.0
0
0
2002
283,000
5,642,000
3,626
2,134
64.8
0%
0
0
0.0
0.0
0
0
2003
289,000
5,931,000
3,729
2,195
66.6
0%
0
0
0.0
0.0
0
0
2004
295,000
6,226,000
3,833
2,256
68.5
0%
0
0
0.0
0.0
0
0
2005
301,000
6,527,000
3,939
2,318
70.4
0%
0
0
0.0
0.0
0
0
2006
307,000
6,834,000
4,046
2,382
72.3
0%
0
0
0.0
0.0
0
0
2007
313,000
7,147,000
4,154
2,445
74.2
0%
0
0
0.0
0.0
0
0
2008
0
7,147,000
4,264
2,510
76.2
60%
2,558
1,506
45.7
4.2
8,023
168,478
2009
0
7,147,000
3,680
2,166
65.8
60%
2,208
1,300
39.5
3.7
6,925
145,423
2010
0
7,147,000
3,209
1,889
57.3
60%
1,925
1,133
34.4
3.2
6,038
126,797
2011
0
7,147,000
2,827
1,664
50.5
60%
1,696
998
30.3
2.8
5,319
111,698
2012
0
7,147,000
2,516
1,481
45.0
60%
1,509
888
27.0
2.5
4,734
99,410
2013
0
7,147,000
2,262
1,331
40.4
60%
1,357
799
24.2
2.2
4,255
89,362
2014
0
7,147,000
2,052
1,208
36.7
60%
1,231
725
22.0
2.0
3,862
81,103
2015
0
7,147,000
1,880
1,106
33.6
60%
1,128
664
20.2
1.9
3,537
74,271
2016
0
7,147,000
1,736
1,022
31.0
60%
1,041
613
18.6
1.7
3,266
68,581
2017
0
7,147,000
1,615
950
28.9
60%
969
570
17.3
1.6
3,038
63,806
2018
0
7,147,000
1,512
890
27.0
60%
907
534
16.2
1.5
2,846
59,763
2019
0
7,147,000
1,425
839
25.5
60%
855
503
15.3
1.4
2,681
56,310
2020
0
7,147,000
1,350
794
24.1
60%
810
477
14.5
1.3
2,540
53,331
2021
0
7,147,000
1,284
756
22.9
60%
770
453
13.8
1.3
2,416
50,735
2022
0
7,147,000
1,226
722
21.9
60%
736
433
13.1
1.2
2,307
48,450
2023
0
7,147,000
1,175
691
21.0
60%
705
415
12.6
1.2
2,210
46,417
2024
0
7,147,000
1,128
664
20.2
60%
677
399
12.1
1.1
2,123
44,591
2025
0
7,147,000
1,087
640
19.4
60%
652
384
11.6
1.1
2,045
42,935
2026
0
7,147,000
1,048
617
18.7
60%
629
370
11.2
1.0
1,972
41,419
2027
0
7,147,000
1,013
596
18.1
60%
608
358
10.9
1.0
1,906
40,020
2028
0
7,147,000
980
577
17.5
60%
588
346
10.5
1.0
1,844
38,719
2029
0
7,147,000
949
559
17.0
60%
569
335
10.2
0.9
1,786
37,501
2030
0
7,147,000
920
542
16.4
60%
552
325
9.9
0.9
1,731
36,354
MODEL INPUT PARAMETERS:	NOTES:
Assumed Methane Content of LFG: 50%	* Maximum power plant capacity assumes a gross heat rate of 10,800 Btus per kW-hr (hhv).
Fast Decay	Slow Decay Total Site Lo **Emission reductions do not include electricity generation, assume a January 1, 2008 system start-up date,
Methane Generation Rate Constant (k): 0.230	0.027 and are calculated using a methane density (at standard temperature and pressure) of 0.000716 Mg/m3.
Methane Generation Potential (Lo) (m3/Mg^ 68	189 91
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2.3 Model Outputs - Graph
Model results are also displayed in graphical form in the "Outputs-Graph" worksheet (see Figure
4 for a sample graph layout). Data displayed in the graph includes the following:
•	Landfill gas generation rates for each projection year in cubic meters per hour
•	Landfill gas recovery rates for each projection year in cubic meters per hour.
•	Actual (historical) landfill gas recovery rates in cubic meters per hour.
As noted in the instructions listed below the graph, the title of the graph will need to be edited by
clicking on the graph title and typing the desired title. The timeline shown in the x-axis will need
editing if the user wishes to not have the projection end in 2030. To edit the x-axis for displaying
an alternative time period, click on the x-axis and select "Format" "x-axis". Then select the
"Scale" tab and input the desired opening and closing year for the projection. Also, because the
graph is linked to the table, it will show data for all projection years shown in the table (given
the limits set for the x-axis). It will not show any hidden rows. If the table shows years beyond
the range set for the x-axis, the line of the graph will appear to go off of the edge of the graph.
To correct this, the user will need to either hide the extra rows or edit the x-axis range to display
the additional years.
To print the graph, click anywhere on the graph and select "File" "Print" OK". If the user does
not click on the graph prior to printing, the instructions will also appear in the printout.
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FIGURE 4. SAMPLE MODEL OUTPUT GRAPH
Figure 1. Iiiogas Generation and Recovery Projection
	Landfill, El Salvador
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
2030
	Landfill Biogas Generation
Predicted Landfill Biosps Recovery • Actual LFG Recovery
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3.0 REFERENCES
EPA, 1991. Regulatory Package for New Source Performance Standards and 111(d) Guidelines
for Municipal Solid Waste Air Emissions. Public Docket No. A-88-09 (proposed May 1991).
Research Triangle Park, NC. U.S. Environmental Protection Agency.
EPA, 1998. Compilation of Air Pollutant Emission Factors, AP-42, Volume 1: Stationary Point
and Area Sources, 5th ed., Chapter 2.4. Office of Air Quality Planning and Standards. Research
Triangle Park, NC. U.S. Environmental Protection Agency.
EPA, 2005. Landfill Gas Emissions Model (LandGEM) Version 3.02 User's Guide. EPA-600/R-
05/047 (May 2005), Research Triangle Park, NC. U.S. Environmental Protection Agency.
IPCC, 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental
Panel on Climate Change (IPCC), Volume 5 (Waste), Chapter 3 (Solid Waste Disposal), Table
3.1.
UNFCCC, 2006. Revision to the approved baseline methodology AM0025,"Avoided from
organic waste through alternative waste treatment processes." United Nations Framework
Convention on Climate Change (UNFCCC), 03 March 2006.
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