EPA-600/R-05/047

May 2005

United States

Environmental Protection

Agency

Landfill Gas Emissions

Model (LandGEM) Version

3.02 User’s Guide

EPA-600/R-05/047

May 2005

Landfill Gas Emissions Model

(LandGEM) Version 3.02 User’s Guide

by

Amy Alexander, Clint Burklin, and Amanda Singleton

Eastern Research Group

Morrisville, NC

Purchase Order No. 3C-R127-NALX

Project Officer: Susan A. Thorneloe

Office of Research and Development

National Risk Management Research Laboratory

Air Pollution Prevention and Control Division

Research Triangle Park, NC 27711

U.S. Environmental Protection Agency

Office of Research and Development

Washington, DC 20460
ii

Abstract

The Landfill Gas Emissions Model (LandGEM) is an automated estimation tool with a

Microsoft Excel interface that can be used to estimate emission rates for total landfill gas,

methane, carbon dioxide, nonmethane organic compounds, and individual air pollutants

from municipal solid waste landfills. This guide provides step-by-step guidance for using

this software application, as well as an appendix containing background information on the

technical basis of LandGEM. LandGEM can use either site-specific data to estimate

emissions or default parameters if no site-specific data are available. The model contains

two sets of default parameters, CAA defaults and inventory defaults. The CAA defaults are

based on federal regulations for MSW landfills laid out by the Clean Air Act (CAA) and can

be used for determining whether a landfill is subject to the control requirements of these

regulations. The inventory defaults are based on emission factors in EPA’s Compilation of

Air Pollutant Emission Factors (AP-42) and can be used to generate emission estimates for

use in emission inventories and air permits in the absence of site-specific test data.
iii

Foreword

The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting

the Nation’s land, air, and water resources. Under a mandate of national environmental laws,

the Agency strives to formulate and implement actions leading to a compatible balance

between human activities and the ability of natural systems to support and nurture life. To meet

this mandate, EPA’s research program is providing data and technical support for solving

environmental problems today and building a science knowledge base necessary to manage

our ecological resources wisely, understand how pollutants affect our health, and prevent or

reduce environmental risks in the future.

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for

investigation of technological and management approaches for preventing and reducing risks

from pollution that threaten human health and the environment. The focus of the Laboratory’s

research program is on methods and their cost-effectiveness for prevention and control of

pollution to air, land, water, and subsurface resources; protection of water quality in public

water systems; remediation of contaminated sites, sediments and ground water; prevention

and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with

both public and private sector partners to foster technologies that reduce the cost of

compliance and to anticipate emerging problems. NRMRL’s research provides solutions to

environmental problems by: developing and promoting technologies that protect and improve

the environment; advancing scientific and engineering information to support regulatory and

policy decisions; and providing the technical support and information transfer to ensure

implementation of environmental regulations and strategies at the national, state, and

community levels.

This publication has been produced as part of the Laboratory’s strategic long-term research

plan. It is published and made available by EPA’s Office of Research and Development to

assist the user community and to link researchers with their clients.

Sally Gutierrez, Acting Director

National Risk Management Research Laboratory
iv

EPA Review Notice

This report has been peer and administratively reviewed by the U.S. Environmental

Protection Agency and approved for publication. Mention of trade names or commercial

products does not constitute endorsement or recommendation for use.

This document is available to the public through the National Technical Information

Service, Springfield, Virginia 22161.
v

Table of Contents

Section Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

List of Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Introduction ............................................................. 1

Overview of How LandGEM Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Understanding LandGEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Spreadsheet Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 First-Order Decomposition Rate Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Software Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.4 Significant Differences Between Model Versions . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.5 Differences Between the Model and AP-42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2. Providing Landfill Characteristics ......................................... 9

2.1 Landfill Name or Identifier ........................................... 9

2.2 Landfill Open Year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.3 Landfill Closure Year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.4 Have Model Calculate Closure Year? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.5 Waste Design Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.6 Landfills Accepting Waste Over 80 Years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Determining Modeling Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1 Methane Generation Rate (k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.2 Potential Methane Generation Capacity (Lo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.3 Nonmethane Organic Compound Concentration . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.4 Methane Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4. Selecting Gases/Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5. Entering Waste Acceptance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6. Printing Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7. Viewing and Printing Tabular Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8. Viewing and Printing Graphical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9. Viewing and Printing Inventory Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

10. Viewing and Printing the Summary Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

11. Additional Information and References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Appendix A Technical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
vi

List of Images

Image Page

1. Macro Security Warning Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Landfill Characteristics Inputs ............................................ 9

3. Model Parameters Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4. Gas/Pollutant Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5. Waste Acceptance Rate Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6. INPUT REVIEW Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7. RESULTS Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8. Graphical Results in Units of Megagrams per Year . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9 INVENTORY Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

List of Tables

Table Page

1. Worksheet Names and Functions in LandGEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Values for the Methane Generation Rate (k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3. Values for the Potential Methane Generation Capacity (Lo) . . . . . . . . . . . . . . . . . . . . 17

4. Gas/Pollutant Default Data Used in LandGEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5. Acceptance Rate Input Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1

Introduction

This document provides step-by-step guidance for using the Landfill Gas Emissions Model

(LandGEM), a software application with a Microsoft Excel interface that estimates air

pollutants and other gases from municipal solid waste (MSW) landfills. Using this

document, you will learn how to

• Enter landfill-specific data,

• Choose between site-specific and default model parameters,

• Estimate emission rates, and

• View and print tabular and graphical results.

Overview of How LandGEM Works

LandGEM is an automated tool for estimating emission rates for total landfill gas, methane,

carbon dioxide, nonmethane organic compounds (NMOCs), and individual air pollutants

from MSW landfills. Landfill owners and operators can use LandGEM to determine if a

landfill is subject to the control requirements of the federal New Source Performance

Standards (NSPS) for new MSW landfills (40 CFR 60 Subpart WWW), the federal Emission

Guidelines (EG) for existing MSW landfills (40 CFR Subpart Cc), or the National Emission

Standards for Hazardous Air Pollutants (NESHAP) for MSW landfills (40 CFR Subpart

AAAA).

LandGEM can use either site-specific data to estimate emissions or default parameters if no

site-specific data are available. LandGEM contains two sets of default parameters.

CAA Defaults—The CAA defaults are based on requirements for MSW landfills

laid out by the Clean Air Act (CAA), including the NSPS/EG and NESHAP. This set

of default parameters yields conservative emission estimates and can be used for

determining whether a landfill is subject to the control requirements of the NSPS/EG

or NESHAP.

Inventory Defaults—With the exception of wet landfill defaults, the inventory

defaults are based on emission factors in the U.S. Environmental Protection
2

Agency’s (EPA’s) Compilation of Air Pollutant Emission Factors (AP-42). This set

of defaults yields average emissions and can be used to generate emission estimates

for use in emission inventories and air permits in the absence of site-specific test

data.

The default parameters in Version 3.02 of LandGEM represent values specified by

NSPS/EG and NESHAP for determining applicability of CAA requirements. Also included

are values specified in AP-42 for developing national and state emission inventories. The

AP-42 values are being updated with new information that has been collected by EPA from

more recent field tests. In addition, research is underway to obtain data for developing

emission factors for wet/bioreactor landfills where leachate and other liquids are added to

accelerate waste decomposition.
3

Section 1.

Understanding LandGEM

LandGEM is based on a first-order decomposition rate equation for quantifying emissions

from the decomposition of landfilled waste in MSW landfills. The software provides a

relatively simple approach to estimating landfill gas emissions. Model defaults are based on

empirical data from U.S. landfills. Field test data can also be used in place of model defaults

when available. Further guidance on EPA test methods, CAA regulations, and other

guidance regarding landfill gas emissions and control technology requirements can be found

at http://www.epa.gov/ttnatw01/landfill/landflpg.html.

LandGEM is considered a screening tool—the better the input data, the better the estimates.

Often, there are limitations with the available data regarding waste quantity and

composition, variation in design and operating practices over time, and changes occurring

over time that impact the emissions potential. Changes to landfill operation, such as

operating under wet conditions through leachate recirculation or other liquid additions, will

result in generating more gas at a faster rate. Defaults for estimating emissions for this type

of operation are being developed to include in LandGEM along with defaults for

conventional landfills (no leachate or liquid additions) for developing emission inventories

and determining CAA applicability. Refer to the Web site identified above for future

updates to LandGEM.

Appendix A provides further background information regarding the technical basis of

LandGEM and how it relates to landfill emissions, methane, carbon dioxide, NMOCs, and

air pollutants.

1.1 Spreadsheet Design

LandGEM consists of nine worksheets within a Microsoft Excel spreadsheet. The worksheet

names and their functions are listed in Table 1.
4

Table 1. Worksheet Names and Functions in LandGEM

Worksheet Name Function

INTRO Contains an overview of the model and important notes about

using LandGEM

USER INPUTS

Allows users to provide landfill characteristics, determine

model parameters, select up to four gases or pollutants (total

landfill gas, methane, carbon dioxide, NMOCs, and 46 air

pollutants), and enter waste acceptance rates

POLLUTANTS Allows users to edit air pollutant concentrations and molecular

weights for existing pollutants and add up to 10 new pollutants

INPUT REVIEW Allows users to review and print model inputs

METHANE Calculates methane emission estimates using the first-order

decomposition rate equation

RESULTS

Shows tabular emission estimates for up to four gases/

pollutants (selected in the USER INPUTS worksheet) in

megagrams per year, cubic meters per year, and user’s choice

of a third unit of measure (average cubic feet per minute, cubic

feet per year, or short tons per year)

GRAPHS

Shows graphical emission estimates for up to four gases/

pollutants (selected in the USER INPUTS worksheet) in

megagrams per year, cubic meters per year, and user’s choice

of a third unit of measure (selected in the RESULTS

worksheet)

INVENTORY Displays tabular emission estimates for all gases/pollutants for

a single year specified by users

REPORT Allows users to review and print model inputs and outputs in a

summary report

1.2 First-Order Decomposition Rate Equation

LandGEM uses the following first-order decomposition rate equation to estimate annual

emissions over a time period that you specify. The model parameters k and Lo used by this

decomposition equation are described further in Section 3.0.
5

Image 1. Macro Security Warning Message.

where

QCH4 = annual methane generation in the year of the calculation (m3/year)

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 (year-1)

Lo = potential methane generation capacity (m3/Mg)

Mi

 = mass of waste accepted in the ith year (Mg)

tij = age of the jth section of waste mass Mi accepted in the ith year (decimal years, e.g.,

3.2 years)

1.3 Software Requirements

LandGEM requires Microsoft Excel 97 or a more recent version of Excel. Earlier versions

of Excel are unable to properly run the model because macros are embedded in the software.

Enable Macros—You must select Enable Macros when prompted (immediately

after opening the file) to allow the LandGEM software to use macros embedded in

the file. LandGEM has been carefully screened and is free of any viruses.

Macro Security—If you are using Microsoft Excel 2000 or Excel 2002 (within the

Microsoft Office XP software package), you must set your Macro Security Level to

Medium prior to opening the software to allow the Enable Macros option to be

selected. If your Macro Security Level is set to High when the model is opened, then

the warning message shown in Image 1 will appear, and the embedded macros

needed to run LandGEM properly will be disabled. You can adjust the Macro

Security Level in Excel by selecting Macro...Security from the Tools menu and

clicking on the Medium radio button. Although LandGEM can operate with the

Macro Security Level set to Low, this setting is not recommended by Microsoft.
6

Memory Requirements—You should have a minimum of 64 megabytes of random

access memory (RAM). In addition, you will need a minimum of 2 megabytes of free

space on your hard drive to accommodate the LandGEM software.

Read Only Feature—LandGEM has been specified as a Read Only file. You save a

copy of LandGEM under a new file name when running each landfill scenario. The

Read Only restriction is intended to protect the original file from being inadvertently

over-written. If necessary, you can remove this restriction by changing the file

properties via a file management program (e.g., Windows Explorer).

Password Protection Feature—To avoid user modifications from occurring within

the model, all of the worksheets contained in LandGEM and the Microsoft Excel

workbook itself have been password protected.

Screen Resolution—The optimum screen resolution for viewing LandGEM is 1024

by 768 pixels. To change the screen resolution, you can open the Control Panel from

the Start menu, open the Display folder, select the Settings tab at the top of the

window, and adjust the Screen resolution or Screen area option (depending on your

version of Windows) accordingly.

1.4 Significant Differences Between Model Versions

LandGEM Version 3.02 replaces Versions 2.01 and 3.01. Significant differences between

Versions 2.01 and 3.02 of LandGEM include:

• Version 3.02 uses a revised first-order decomposition rate equation that improves the

accuracy of emission estimates over time, especially for landfills being modeled

using higher methane generation rate (k) values. The equation used in Version 2.01

integrates emissions over each year, whereas the revised equation in Version 3.02

integrates emissions over a 0.1 year time increment. This revision is considered an

improvement over the previous calculation methodology. This new equation in

Version 3.02 results in slightly lower emission estimates than previous versions for

typical k values. For example, Version 3.02 emission estimates are 2% lower for a k

of 0.05 year-1 (CAA Conventional) and 1% lower for a k of 0.02 year-1 (CAA Arid

Area). Version 3.02 estimates significantly lower emissions for higher k values—for

example, 25% lower for a k of 0.7 year-1 (Inventory Wet).
7

• Version 3.02 allows users to model emissions of total landfill gas, which can be

calibrated using a user-specified methane content other than 50 percent. In Version

2.01, users cannot estimate total landfill gas emissions directly and must calculate

total landfill gas off-line using methane emission estimates.

• Version 2.01 uses metric units of measure exclusively, whereas Version 3.02 allows

users to choose between several English (e.g., short tons, cubic feet) and metric (e.g.,

megagrams, cubic meters) units of measure for model inputs and outputs.

• Version 2.01 reports emissions for 200 years past closure year of the landfill,

whereas Version 3.02 reports emissions for 140 years total.

• Version 2.01 does not allow waste to be accepted in the closure year. To provide

users with more flexibility when entering inputs, Version 3.02 was changed to allow

waste to be accepted in the closure year.

• Version 2.01 contains AP-42 default values and air pollutant concentrations and

molecular weights that were current as of September 1997 (Supplement C of the 5th

Edition). Version 3.02 contains revised AP-42 default values (within the inventory

defaults), air pollutant concentrations, and molecular weights that are current as of

November 1998 (Supplement E of the 5th Edition).

• Version 3.02 incorporates inventory default k and Lo values for wet landfills (such as

bioreactors).

• Version 3.02 replaces Version 3.01 by correcting an error when av ft3

/min or ft3/year

is selected as the user-specified unit in the RESULTS worksheet.

1.5 Differences Between the Model and AP-42

Significant differences between Version 3.02 of LandGEM and EPA’s Compilation of Air

Pollutant Emission Factors (AP-42) include:

• The inventory default values for NMOC concentration and several air pollutant

concentrations used in Version 3.02 of LandGEM differ slightly from those in the

November 1998 version (Supplement E of the 5th Edition) of AP-42. These minor

differences are due to rounding of the concentration values to more accurately reflect

their relative uncertainty. These rounding differences are expected to be rectified in
8

an upcoming revision of AP-42 for MSW landfills because the uncertainty of the

values within the current version of AP-42 do not accurately correspond with the

inherent uncertainty of the NMOC and air pollutant concentrations.

• Due to a revision in the first-order decomposition rate equation used in Version 3.02

of LandGEM (Section 1.4), the methane generation equation (Equation 1) within

AP-42 no longer matches the equation used by LandGEM. Differences between the

two calculation methodologies are expected to be rectified in an upcoming revision

of AP-42 for MSW landfills.
9

Image 2. Landfill Characteristics Inputs.

Section 2.

Providing Landfill Characteristics

Enter data on the USER INPUTS worksheet that relate to the identity and size of the landfill

being modeled.

• Landfill name or identifier,

• Landfill open year,

• Landfill closure year,

• Option to have model calculate closure year, and

• Waste design capacity.

Image 2 shows these inputs as they appear on the USER INPUTS worksheet. To clear all of

the landfill characteristic inputs, gas/pollutant selections (see Section 4.0), and waste

acceptance rate data (see Section 5.0), click on Clear ALL Non-Parameter Inputs/Selections

in the USER INPUTS worksheet. These inputs will then return to their defaults.

2.1 Landfill Name or Identifier

Use the Landfill Name or Identifier to enter a landfill’s name and scenario information (for

example, “Landfill A - Closed Cells” or “Landfill A - Leachate Recirculation Cells”). You

can also enter information about the landfill as it relates to the types of model parameters

chosen (for example, “Landfill B - NSPS/EG Conventional k Value” or “Landfill B - Userspecified k = 0.06”). Model parameters are discussed further in Section 3.0. The Landfill

Name or Identifier entry box is limited to 50 characters.
10

The Landfill Name or Identifier you enter on the USER INPUTS worksheet is shown in the

same location on other worksheets within LandGEM. You are not required to enter

information into the Landfill Name or Identifier entry box. The Landfill Name or Identifier

entry box is not affected by the Clear ALL Non-Parameter Inputs/Selections button.

2.2 Landfill Open Year

Landfill Open Year is a required input and represents the year that the landfill began

accepting waste. The open year should be in a four-digit year format (e.g., 2004).

2.3 Landfill Closure Year

Landfill Closure Year represents either of the following in LandGEM:

• Final year the landfill accepted waste, or

• Year the landfill is expected to reach Waste Design Capacity.

LandGEM uses the closure year of the landfill to determine the final year the landfill has

accepted or is planning to accept waste. The “permitted” closure year of the landfill does not

always represent the same year the landfill ceases to accept waste.

Landfill Closure Year is not a required input. However, if Landfill Closure Year is unknown,

then you must select Yes for the Have Model Calculate Closure Year? option, AND you

must enter Waste Design Capacity. If you enter a closure year, but still select Yes for the

option to have the model calculate closure year, then the model will disregard the closure

year you entered and automatically calculate closure year for you.

The model limits the number of years for entering Waste Acceptance Rates to 80 years (see

Section 5.0 for further discussion about Waste Acceptance Rates). If the Landfill Closure

Year entered is greater than 80 years from the Landfill Open Year entered (i.e., over 80 years

of waste acceptance), then the model will disregard the Landfill Closure Year entered and

will assign the 80th year past the Landfill Open Year as the final year of waste acceptance (or

the closure year) used by the model to estimate emissions. For example, if you enter a

Landfill Open Year of 1940, a Landfill Closure Year of 2030, and Waste Acceptance Rates

for 1940-2004, then the model will only allow Waste Acceptance Rates to be entered for

2005 to 2019 and will calculate emissions as though the landfill closed in 2019. See Section

2.6 for instructions on estimating total emissions properly for scenarios where landfills

accept waste beyond the waste acceptance limit of 80 years.
11

Calculated landfill closure year Waste design capacity Waste acceptance rates

Final waste acceptance rate in 2000

Year of final waste acceptance rate

= − ∑

+

⎡

⎣

⎢ ⎤

⎦

⎥

( ( ))

Calculated landfill closure year

5 000 000 short tons 4 100 000 short tons

200 000 short tons 2000

2005

= − +

=

⎡

⎣

⎢ ⎤

⎦

⎥

(, , , , )

,

2.4 Have Model Calculate Closure Year?

If Landfill Closure Year is unknown, select Yes for the option to have the model calculate

closure year. The default option is No. You must enter the Waste Design Capacity if you

want the model to calculate closure year for you. Waste Design Capacity is discussed further

in Section 2.5.

If you allow LandGEM to determine the closure year, it does so based on Landfill Open

Year, Waste Design Capacity, and Waste Acceptance Rates you entered. Essentially,

LandGEM calculates the closure year by summing the Waste Acceptance Rates entered,

subtracting this “waste-in-place” amount from the Waste Design Capacity entered, and then

dividing by the final (or most recent) acceptance rate entered. The model assumes that your

final waste acceptance rate entered will continue to be the annual amount of waste accepted

until closure of the landfill or until there are 80 years of waste acceptance, whichever

scenario comes first (see Section 5.0 for further discussion about Waste Acceptance Rates).

Example 1 illustrates how the model calculates the closure year if it is unknown.

Example 1. Scenario for Unknown Landfill Closure Year

Landfill open year = 1970

Landfill closure year = ?

Have model calculate closure year? = Yes

Waste design capacity = 5,000,000 short tons

Waste acceptance rate from 1970 to 1990 = 100,000 short tons/year

Waste acceptance rate from 1991 to 2000 = 200,000 short tons/year

The model limits the number of years for entering Waste Acceptance Rates to 80 years (see

Section 5.0 for further discussion about Waste Acceptance Rates). If the Waste Design

Capacity has not been reached by the 80th year of waste acceptance, then the model will

assign the 80th year past the Landfill Open Year entered as the final year of waste acceptance

(or the closure year) used by the model to estimate emissions. For example, if you allow the
12

model to calculate closure year and enter a Landfill Open Year of 1960, a Waste Design

Capacity of 10,000,000 Mg, and Waste Acceptance Rates of 100,000 Mg/year for

1960S2004, then the model will calculate emissions as though the landfill closed in 2039

because that is when it will reach the 80-year limit of waste acceptance. See Section 2.6 for

instructions on estimating total emissions properly for scenarios where landfills accept waste

beyond the waste acceptance limit of 80 years.

2.5 Waste Design Capacity

Waste Design Capacity represents the total amount of waste that can be disposed of in the

landfill, or the amount of “waste-in-place” upon closure. Enter Waste Design Capacity only

when you select Yes for the Have Model Calculate Closure Year? option. If you enter Waste

Design Capacity without selecting Yes, the model will simply disregard the capacity amount

you entered.

Waste Design Capacity can be entered in metric units of megagrams or English units of

short tons. (Note: One megagram is equivalent to one metric ton.) Select the units of

measure using the drop-down menu. The default unit of measure for Waste Design Capacity

is megagrams.

Landfill gas emission factors were developed using empirical data from U.S. MSW landfills.

The composition of waste in the landfills reflects U.S. waste composition including MSW,

inert material, and other non-hazardous waste streams. If a portion of the landfill contains

primarily non-biodegradable waste (i.e., inert material), such as ash from waste combustion,

this portion may be subtracted from the Waste Design Capacity, depending upon

documentation and approval from a regulatory authority. However, this is not recommended

for sites that are typical of MSW landfills, which contain a range of waste that may or may

not be degradable. This is because the emission factors were developed relating total waste

quantity to total quantity of landfill gas.

2.6 Landfills Accepting Waste Over 80 Years

Sections 2.3 and 2.4 explain scenarios where LandGEM will implement a waste acceptance

limit of 80 years in order to estimate emissions properly. If you are modeling a landfill that

either has accepted or will accept waste for over 80 years, then multiple model runs are

required to calculate emissions for the entire waste acceptance lifetime of the landfill. You

should associate a unique file name and Landfill Name or Identifier in the USER INPUTS

worksheet for each model run to properly identify the order of the model runs (“Landfill X -

Run 1 of 2” and “Landfill X - Run 2 of 2,” for example).
13

When the 80-year waste acceptance limit is exceeded, the INPUT REVIEW worksheet

reports the actual landfill closure year that would be reached in absence of the 80-year limit.

The additional years of waste acceptance can be modeled in a successive model run in order

to capture the total emissions from the actual waste acceptance lifetime. The METHANE

worksheet provides the waste-in-place amount at the end of the initial 80 years and

remaining waste capacity from the final year of the initial model run if you have chosen to

have model calculate closure year. These values can be used as inputs for the second model

run. Once both model runs have been completed, then the emissions on the RESULTS

worksheet from each run can be summed together by year for each gas/pollutant to result in

total emissions for the actual waste acceptance lifetime of the landfill.

Example 2 outlines a scenario for running LandGEM multiple times in order to accurately

represent the emissions for landfills accepting waste over 80 years.
14

Example 2. Scenario for Landfills Accepting Waste Over 80 Years

First Model Run Inputs on USER INPUTS Worksheet:

Landfill open year = 1940

Landfill closure year = ?

Have model calculate closure year? = Yes

Waste design capacity = 12,000,000 Mg

Waste acceptance rate from 1940 to 2000 = 100,000 Mg/year

Waste acceptance rate from 2001 to 2004 = 200,000 Mg/year

First Model Run Results on METHANE Worksheet:

Closure year (with 80-year limit) = 2019

Actual closure year (without limit) = 2030

Calculated waste acceptance rate from 2005 to 2019 = 200,000 Mg/year

Waste-in-place at start of next model run = 9,900,000 Mg

Capacity remaining at start of next model run = 2,100,000 Mg

Second Model Run Inputs on USER INPUTS Worksheet:

Landfill open year = 2020 [One year past closure year from the first model run]

Landfill closure year = ?

Have model calculate closure year? = Yes

Waste design capacity = 2,100,000 Mg [Capacity remaining from the first model run]

Waste acceptance rate for 2020 = 200,000 Mg/year [Calculated waste acceptance rate from the

first model run]

Second Model Run Results on METHANE Worksheet:

Closure year (with 80-year limit) = Actual closure year (without limit) = 2030

Total annual emissions for each gas/pollutant = (Run 1 emissions) + (Run 2 emissions)

For example, methane emissions for 2021 = 2.586×107

 + 1.662×106 = 2.752×107
15

Image 3. Model Parameters Inputs.

Section 3.

Determining Model Parameters

LandGEM relies on several model parameters to estimate landfill emissions.

• Methane generation rate (k),

• Potential methane generation capacity (Lo),

• NMOC concentration, and

• Methane content.

Default values for the model parameter inputs on the USER INPUTS worksheet are shown

in Image 3. Model parameters should be selected using consistent default options. For

example, if “Inventory Conventional - 0.04” is chosen for k, then “Inventory Conventional -

100” should be selected for Lo and “Inventory No or Unknown Co-disposal - 600” or

“Inventory Co-disposal - 2,400” should be selected for NMOC Concentration. When using

LandGEM to determine whether a landfill is subject to the control requirements of the

NSPS/EG or NESHAP, CAA defaults must be chosen for all four model parameters.

You may select each of the model parameters from the drop-down menu. Alternatively, you

may enter site-specific model parameter values other than the default values based on field
16

data or other information. Select User-specified for the model parameter for which you

would like to enter site-specific data. A User-specified value entry box will appear to the

right of that parameter and you can enter the site-specific value. User-specified value entry

boxes only appear when User-specified is selected from the drop-down menu for a particular

model parameter.

Clicking on Restore Default Model Parameters in the USER INPUTS worksheet resets all

four of the model parameters back to their default values (shown in Image 3) and removes

any user-specified values entered.

3.1 Methane Generation Rate (k)

The Methane Generation Rate, k, determines the rate of methane generation for the mass of

waste in the landfill. The higher the value of k, the faster the methane generation rate

increases and then decays over time. The value of k is primarily a function of four factors:

• Moisture content of the waste mass,

• Availability of the nutrients for microorganisms that break down the waste to form

methane and carbon dioxide,

• pH of the waste mass, and

• Temperature of the waste mass.

Use EPA Method 2E to determine site-specific k values for user-specified data. The k value,

as it is used in the first-order decomposition rate equation, is in units of 1/year, or year-1. The

five k values used by LandGEM are shown in Table 2. Arid area landfills are located in

areas that receive less than 25 inches of rainfall per year. The default k value is the CAA k

value for conventional landfills.

Table 2. Values for the Methane Generation Rate (k).

Default Type Landfill Type k Value

year-1

CAA Conventional 0.05 (default)

CAA Arid Area 0.02

Inventory Conventional 0.04

Inventory Arid Area 0.02

Inventory Wet (Bioreactor) 0.7
17

3.2 Potential Methane Generation Capacity (Lo)

The Potential Methane Generation Capacity, Lo, depends only on the type and composition

of waste placed in the landfill. The higher the cellulose content of the waste, the higher the

value of Lo. The default Lo values used by LandGEM are representative of MSW. The Lo

value, as it is used in the first-order decomposition rate equation, is measured in metric units

of cubic meters per megagram to be consistent with the CAA. The five Lo values used by

LandGEM are shown in Table 3. The default Lo value is the CAA Lo value for conventional

landfills.

Table 3. Values for the Potential Methane Generation Capacity (Lo).

Emission Type Landfill Type Lo Value -

m3

/Mg

CAA Conventional 170 (default)

CAA Arid Area 170

Inventory Conventional 100

Inventory Arid Area 100

Inventory Wet (Bioreactor) 96

3.3 Nonmethane Organic Compound Concentration

The NMOC Concentration in landfill gas is a function of the types of waste in the landfill

and the extent of the reactions that produce various compounds from the anaerobic

decomposition of waste. NMOC Concentration is measured in units of parts per million by

volume (ppmv) and is used by LandGEM only when NMOC emissions are being estimated.

The NMOC Concentration for the CAA default is 4,000 ppmv as hexane. The NMOC

Concentration for the inventory default is 600 ppmv where co-disposal of hazardous waste

has either not occurred or is unknown and 2,400 ppmv where co-disposal of hazardous

waste has occurred.

The default NMOC Concentration is the CAA value. If you use a site-specific value for

NMOC concentration, then you must correct for air infiltration. EPA Method 25C is

recommended for obtaining a site-specific concentration of NMOCs.

3.4 Methane Content

For LandGEM, landfill gas is assumed to be 50 percent methane and 50 percent carbon
18

QQ P CO CH CH 24 4 =× − { } [ ] 1 100 1 ( )

( )

[ ] ( )

{ } [ ] ( )

QQQ

QQ P

Q QQ QP Q

QQ P

total CH CO

CH total CH

CO total CH CH CH CH

CO CH CH

= +

= ×

=−= −

=× −

4 2

4 4

2 4 44 4

24 4

100

100

1 100 1

dioxide, with additional, trace constituents of NMOCs and other air pollutants. When using

LandGEM for complying with the CAA, Methane Content must remain fixed at 50 percent

by volume (the model default value).

You may choose other methane amounts for the Methane Content using the User-specified

selection if data exist to support using another concentration. However, using LandGEM at

landfills that have methane content outside the range of 40 to 60 percent is not

recommended. The first-order decomposition rate equation used by LandGEM to determine

emissions may not be valid outside of this range.

The production of methane is determined using the first-order decomposition rate equation

and is not affected by the concentration of methane. However, the concentration of methane

affects the calculated production of carbon dioxide. The production of carbon dioxide (QCO2)

is calculated from the production of methane (QCH4) and the methane content percentage

(PCH4) using the equation

This equation is derived as follows:

where Qtotal is the total production of landfill gas.
19

Section 4.

Selecting Gases/Pollutants

You can choose four gases or air pollutants to be modeled at one time. The gases and

pollutants to choose from and data associated with them are shown in Table 4.

Table 4. Gas/Pollutant Default Data Used in LandGEM.

Gas/Pollutant Concentration

(ppmv)

Molecular

Weight Notes

Gases

Total landfill gas Not applicable 30.03

Methane Not applicable 16.04

Carbon dioxide Not applicable 44.01

NMOCs

4,000 for CAA

86.18

600 for Inventory No or

Unknown Co-disposal

2,400 for Inventory

Co-disposal

Pollutants:

1,1,1-Trichloroethane (methyl chloroform) 0.48 133.41 A

1,1,2,2-Tetrachloroethane 1.1 167.85 A, B

1,1-Dichloroethane (ethylidene dichloride) 2.4 98.97 A, B

1,1-Dichloroethene (vinylidene chloride) 0.20 96.94 A, B

1,2-Dichloroethane (ethylene dichloride) 0.41 98.96 A, B

1,2-Dichloropropane (propylene dichloride) 0.18 112.99 A, B

2-Propanol (isopropyl alcohol) 50 60.11 B

Acetone 7.0 58.08

Acrylonitrile 6.3 53.06 A, B

Benzene 1.9 for No or Unknown Co-disposal 78.11 A, B 11 for Co-disposal

Bromodichloromethane 3.1 163.83 B

Butane 5.0 58.12 B

Carbon disulfide 0.58 76.13 A, B

Carbon monoxide 140 28.01
Table 4. Gas/Pollutant Default Data Used in LandGEM (Concluded)

20

Carbon tetrachloride 4.0×10-3 153.84 A, B

Carbonyl sulfide 0.49 60.07 A, B

Chlorobenzene 0.25 112.56 A, B

Chlorodifluoromethane 1.3 86.47

Chloroethane (ethyl chloride) 1.3 64.52 A, B

Chloroform 0.03 119.39 A, B

Chloromethane 1.2 50.49 B

Dichlorobenzene 0.21 147 B, C

Dichlorodifluoromethane 16 120.91

Dichlorofluoromethane 2.6 102.92 B

Dichloromethane (methylene chloride) 14 84.94 A

Dimethyl sulfide (methyl sulfide) 7.8 62.13 B

Ethane 890 30.07

Ethanol 27 46.08 B

Ethyl mercaptan (ethanethiol) 2.3 62.13 B

Ethylbenzene 4.6 106.16 A, B

Ethylene dibromide 1.0×10-3 187.88 A, B

Fluorotrichloromethane 0.76 137.38 B

Hexane 6.6 86.18 A, B

Hydrogen sulfide 36 34.08

Mercury (total) 2.9×10-4 200.61 A

Methyl ethyl ketone 7.1 72.11 A, B

Methyl isobutyl ketone 1.9 100.16 A, B

Methyl mercaptan 2.5 48.11 B

Pentane 3.3 72.15 B

Perchloroethylene (tetrachloroethylene) 3.7 165.83 A

Propane 11 44.09 B

t-1,2-Dichloroethene 2.8 96.94 B

Toluene 39 for No or Unknown Co-disposal 92.13 A, B 170 for Co-disposal

Trichloroethylene (trichloroethene) 2.8 131.40 A, B

Vinyl chloride 7.3 62.50 A, B

Xylenes 12 106.16 A, B

A. Hazardous air pollutants (HAP) listed in Title III of the 1990 Clean Air Act Amendments.

B. Considered volatile organic compounds (VOC), as defined by U.S. EPA in 40 CFR 51.100(s).

C. Source tests did not indicate whether this compound was the para- or ortho- isomer. The para- isomer is a Title IIIlisted HAP.

Concentrations, molecular weights, and notes for NMOCs and the 46 air pollutants

contained in Table 4 are from Tables 2.4-1 and 2.4-2 of AP-42 (November 1998 version).

These default pollutant concentrations have already been corrected for air infiltration, as

stated in AP-42. If you use a site-specific value for NMOC Concentration, then you must
21

Image 4. Gas/Pollutant Inputs.

correct for air infiltration.

As discussed in Section 3.3, the NMOC Concentration for the inventory default is 600 ppmv

where co-disposal of hazardous waste has either not occurred or is unknown and 2,400

ppmv where co-disposal of hazardous waste has occurred. Similarly, benzene and toluene

have different concentrations depending upon the co-disposal status of the landfill. Both no

or unknown co-disposal and co-disposal concentrations are shown in Table 4 for these

pollutants.

The molecular weight of landfill gas was estimated using a weighted average of the

molecular weights for methane and carbon dioxide. The molecular weight of 30.03

represents landfill gas as 50 percent methane and 50 percent carbon dioxide. If the Methane

Content model parameter is changed to a value other than 50 percent, then the molecular

weight of total landfill gas is adjusted to represent the appropriate methane content.

Image 4 shows where you can select four gases or pollutants on the USER INPUTS

worksheet. Each of the gas or pollutant entries can be selected from the drop-down menus.
22

The Edit Existing or Add New Pollutant Parameters button in the USER INPUTS worksheet

allows you to change the default pollutant parameters, including concentrations and

molecular weights, for any of the 46 air pollutants listed on the drop-down menus, as well as

add new pollutants and corresponding parameters. Clicking on the Edit Existing or Add New

Pollutant Parameters button lets you view and edit the default parameters for existing

pollutants in the POLLUTANTS worksheet. The default parameters shown on the

POLLUTANTS worksheet are identical to the ones in Table 4. In addition, there are entry

boxes at the bottom of the POLLUTANTS worksheet where you can enter new pollutants

and corresponding concentrations and molecular weights. The Enter New Pollutant

Parameters and Edit Existing Pollutant Parameters buttons at the top of the POLLUTANTS

worksheet help guide you through this worksheet.

The model does not allow you to edit default parameters for total landfill gas, methane,

carbon dioxide, or NMOCs, nor does it allow you to change names of existing pollutants. To

restore the default pollutant parameters for existing pollutants and remove any new

pollutants you may have added, click on the Restore Default Pollutant Parameters button in

the USER INPUTS worksheet. Clicking this button also returns the gas/pollutant drop-down

menus in the USER INPUTS worksheet to their default selections.

In the Description/Comments entry box, you can enter detailed information about the

landfill or the scenario you are modeling. The Description/Comments entry box is limited to

450 characters.

To clear all of the gas/pollutant selections (but not the pollutant parameters) and the landfill

characteristics and waste acceptance rate inputs (see Section 5.0), click on Clear ALL NonParameter Inputs/Selections in the USER INPUTS worksheet. The gas/pollutant drop-down

menus will return to their default selections, as shown in Image 4. The

Description/Comments box is not affected by the Clear ALL Non-Parameter

Inputs/Selections button.
23

Image 5. Waste Acceptance Rate Inputs.

Section 5.

Entering Waste Acceptance Data

Waste Acceptance Rates must be entered in the USER INPUTS worksheet for LandGEM to

properly estimate emissions. Enter annual acceptance rates for each year listed in the Waste

Acceptance Rates table from the Landfill Open Year to the current year or the Landfill

Closure Year. The Waste Acceptance Rates table is shown in Image 5. Once you enter the

Landfill Open Year, the year column of the Waste Acceptance Rates table automatically

shows the years for which acceptance rate data are needed.

You may enter Waste Acceptance Rates in metric units of megagrams per year or English

units of short tons per year by selecting from the drop-down menu. The default unit of

measure for Waste Acceptance Rates is megagrams per year. If you enter acceptance rates in
24

units of megagrams per year, then LandGEM automatically calculates and displays the

acceptance rates in units of short tons per year. Likewise, if you enter acceptance rates in

short tons per year, then LandGEM automatically calculates and displays acceptance rates in

megagrams per year.

The model makes the assumptions outlined in Table 5. regarding data entered in the Waste

Acceptance Rates table.

Table 5. Acceptance Rate Input Options.

If you... Then LandGEM will...

Enter acceptance rates beyond the

Landfill Closure Year you entered,

Ignore the acceptance rates you entered past the

Landfill Closure Year.

Enter acceptance rates through the

current year but not up to the Landfill

Closure Year you entered,

Apply the final (or most recent) acceptance rate

you entered to the years between the current

year and the Landfill Closure Year.

Enter acceptance rates through the

current year and choose to have the

model calculate closure year,

Apply the final (or most recent) acceptance rate

you entered to each successive year not having

an acceptance rate until the waste design

capacity is reached. A smaller acceptance rate

may be used the last year to achieve the exact

design capacity. The final year the landfill

receives waste becomes the closure year.

The model limits the number of years for entering Waste Acceptance Rates to 80 years. See

Section 2.6 for instructions on estimating total emissions properly for scenarios where

landfills accept waste beyond the waste acceptance limit of 80 years.

Landfill gas emission factors were developed using empirical data from U.S. MSW landfills.

The composition of waste in the landfills reflects U.S. waste composition including MSW,

inert material, and other non-hazardous waste streams. For a landfill that may have a portion

containing non-biodegradable waste (i.e., inert material), such as ash from waste

combustion, this portion may be subtracted from the Waste Acceptance Rates depending on

documentation and approval from a regulatory authority. However, this is not recommended

for sites that are typical of MSW landfills containing a range of waste that may or may not

be degradable. This is because the emission factors were developed relating total waste

quantity to total quantity of landfill gas.
25

To clear all entries in the Waste Acceptance Rates table, in addition to landfill

characteristics inputs and gas/pollutant selections, click on Clear ALL Non-Parameter

Inputs/Selections in the USER INPUTS worksheet. The Waste Acceptance Rates table then

returns to its defaults, as shown in Image 5.
26
27

Image 6. INPUT REVIEW Worksheet.

Section 6.

Printing Inputs

To review your inputs as they will be used by LandGEM, go to the INPUT REVIEW

worksheet. All data entered in the USER INPUTS worksheet as well as inputs determined

by the model, such as calculated landfill closure year and waste acceptance rates as they are

interpreted by LandGEM, appear on the INPUT REVIEW worksheet. Image 6 shows a

scenario where closure year is unknown.

To print the INPUT REVIEW worksheet, select Print... from the File menu. The INPUT

REVIEW worksheet is set to print on one page. However, you may adjust this, as well as

other print settings, by selecting Page Setup... from the File menu.
28
29

Image 7. RESULTS Worksheet.

Section 7.

Viewing and Printing Tabular Results

To view emission estimates in a tabular format, go to the RESULTS worksheet. When

comparing results from LandGEM with measurements of extracted gas collected at a site,

the landfill owner or operator must adjust for air infiltration prior to any comparisons. Image

7 displays the RESULTS worksheet for the scenario shown in Image 6.

Data on the RESULTS worksheet include

• Landfill closure year (provided on USER INPUTS worksheet or calculated),

• Methane content from USER INPUTS worksheet,

• Years of waste acceptance from open year to closure year of the landfill,

• Annual waste acceptance rates used by the model in megagrams per year and short
30

tons per year,

• Annual waste-in-place amounts based on acceptance rates used by the model, in

megagrams and short tons,

• Annual emission estimates for the four gases/pollutants selected on the USER

INPUTS worksheet in megagrams per year, cubic meters per year, and a third

measurement unit that you may select from the drop-down menu. The third unit of

measure options are average cubic feet per minute, cubic feet per year, and short tons

per year. LandGEM uses average cubic feet per minute as the default third unit.

To print the RESULTS worksheet, select Print... from the File menu. The RESULTS

worksheet is set to print on one page. However, you may adjust this as well as other print

settings by selecting Page Setup... from the File menu.

Formatting of the values contained in the RESULTS worksheet is protected from user

modification. To adjust the number formats of the values contained in the RESULTS

worksheet, you will need to copy and paste the emission estimates into a new Microsoft

Excel file by following the instructions below:

1. Highlight cells A7 to Q149 and select Copy from the Edit menu,

2. Open a new Microsoft Excel file by selecting New... (Blank Workbook) from the File

menu,

3. Select Paste Special... from the Edit menu and click on the Values radio button in the

Paste Special window that appears.

4. You can now change the number formats of these emission values by selecting

Cells...Number from the Format menu.

It is important to note that when the Methane Content is assumed to be 50 percent by

volume (default), then methane and carbon dioxide emission rates are identical on a volume

basis (e.g., cubic meters per year, average cubic feet per minute, cubic feet per year) because

carbon dioxide is also assumed to be 50 percent by volume. However, methane and carbon

dioxide emission rates will differ from one another on a mass basis (e.g., megagrams per

year, short tons per year) because methane and carbon dioxide have different molecular

weights and, thus, different mass emissions.
31

Image 8. Graphical Results in Units of Megagrams per Year.

Section 8.

Viewing and Printing Graphical Results

To view the emission estimates in a graphical format, go to the GRAPHS worksheet. Image

8 contains one of the three graphs generated on the GRAPHS worksheet for the scenario

shown in Image 6.

A total of three graphs are generated for each scenario, one for each unit of measure of

emissions on the RESULTS worksheet. The top two graphs are in units of megagrams per

year and cubic meters per year, respectively. The third graph represents the units you
32

selected on the RESULTS worksheet (see Section 7.0 for further discussion), which defaults

to average cubic feet per minute. The emission estimates for all four gases or pollutants are

shown on each of the three graphs using a different color to represent each gas or pollutant’s

emissions.

To print the GRAPHS worksheet, select Print... from the File menu. The GRAPHS

worksheet is set to print on one page. However, you may adjust this as well as other print

settings by selecting Page Setup... from the File menu.

Editing and formatting of the graphs are protected from user modification. To create graphs

that can be edited or formatted, you will need to copy and paste the emission estimates from

the RESULTS worksheet or the INVENTORY worksheet into a new Microsoft Excel file by

following the instructions below.

1. Highlight the cells containing the values to be graphed and select Copy from the Edit

menu.

2. Open a new Microsoft Excel file by selecting New... (Blank Workbook) from the File

menu.

3. Select Paste Special... from the Edit menu and click on the Values radio button in the

Paste Special window that appears.

4. You can now create graphs from these emission values by selecting Chart... from the

Insert menu and following the instructions in the Chart Wizard window.
33

Image 9. INVENTORY Worksheet.

Section 9.

Viewing and Printing Inventory Results

To view emission estimates for use in emission inventories and air permits, go to the

INVENTORY worksheet. This worksheet allows you to view and print emission estimates

for a particular year for all gases or pollutants in megagrams per year, cubic meters per year,

average cubic feet per minute, cubic feet per year, and short tons per year. You must enter a

valid four-digit year in the designated entry box to obtain estimates for a particular year. The

inventory year entered must be between the year after the Landfill Open Year entered and

140 years past the Landfill Open Year. Image 9 displays the INVENTORY worksheet for

the scenario shown in Image 6.
34

To print the INVENTORY worksheet, select Print... from the File menu. The INVENTORY

worksheet is set to print on one page. However, you may adjust this as well as other print

settings by selecting Page Setup... from the File menu.

Formatting of the values contained in the INVENTORY worksheet is protected from user

modification. To adjust the number formats of the values contained in the INVENTORY

worksheet, you will need to copy and paste the emission estimates into a new Microsoft

Excel file by following the instructions below:

1. Highlight cells B5 to K68 and select Copy from the Edit menu.

2. Open a new Microsoft Excel file by selecting New... (Blank Workbook) from the File

menu.

3. Select Paste Special... from the Edit menu and click on the Values radio button in the

Paste Special window that appears.

4. You can now change the number formats of these emission values by selecting

Cells...Number from the Format menu.
35

Section 10.

Viewing and Printing the Summary Report

To view the summary report, go to the REPORT worksheet. Information contained in the

summary report on the RESULTS worksheet includes

• A cover page showing the LandGEM title screen (pop-up introduction window that

includes the model version and date), Landfill Name or Identifier and

Description/Comments entered in the USER INPUTS worksheet, the current date,

the first-order decomposition rate equation used to estimate emissions, and a general

description of the model,

• Data contained in the INPUT REVIEW worksheet, including landfill characteristics,

model parameters, gases/pollutants selected, waste acceptance rates, and yearly

waste-in-place amounts,

• Emission estimates in graphical format, as shown on the GRAPHS worksheet, and

• Emission estimates in tabular format, from the RESULTS worksheet.

To print the REPORT worksheet, select Print... from the File menu. The REPORT

worksheet is set to print on seven pages. However, you may adjust this as well as other print

settings by selecting Page Setup... from the File menu.
36
37

Section 11.

Additional Information and References

Additional Information

For further information regarding landfill gas emissions, please access the following Web

sites and documents:

• Rules and Implementation Information for Standards of Performance for MSW

Landfills. EPA, Technology Transfer Network, Air Toxics Website:

http://www.epa.gov/ttnatw01/landfill/landflpg.html.

The following topics are included on this Web site:

- Proposed and Promulgated Rules, including the NSPS/EG requirements,

- Closely Related Rules, Policies or Program Guidance,

- Technical Information, including Background Information Document

(BID)/Response to Comments, Fact Sheets, and Risk Assessment,

- Implementation and Enabling Documents,

- Emission Estimation Tools, including the LandGEM software,

- Source Identification and Location,

- Outreach and Training Materials,

- Permitting,

- Compliance and Enforcement.

• NESHAP Rule and Implementation Information for Municipal Solid Waste Landfills.

EPA, Technology Transfer Network, Air Toxics Website:

http://www.epa.gov/ttnatw01/landfill/lndfillpg.html.

The following topics are included on this Web site:

- Proposed and Promulgated Rules, including the NESHAP requirements,

- Closely Related Rules, Policies or Program Guidance,

- Technical Information, including Background Information Document

(BID)/Response to Comments, Fact Sheets, and Economic Analysis,

- Implementation Documents,

- Source Identification and Location,

- Outreach and Training Materials,
38

- Permitting,

- Compliance and Enforcement.

• Compilation of Air Pollutant Emission Factors (AP-42), Volume 1: Stationary Point

and Area Sources, 5th ed., Chapter 2.4: Municipal Solid Waste Landfills. EPA,

Office of Air Quality Planning and Standards. Research Triangle Park, NC.

http://www.epa.gov/ttn/chief/ap42/ch02/final/c02s04.pdf.

• Use of Landfill Gas Generation Model to Estimate VOC Emissions from Landfills.

Memorandum from Y.C. McGuinn, Radian Corporation, to Susan Thorneloe, EPA.

June 21, 1988. Public Docket No. A-88-09.

• Sensitivity Analysis of Landfill Gas Generation Model. Memorandum from Y.C.

McGuinn, Radian Corporation, to Susan Thorneloe, EPA. June 21, 1988. Public

Docket No. A-88-09.

• Methodology Used to Revise the Model Inputs in the Municipal Solid Waste

Landfills Input Database (Revised). Memorandum from W.R. Pelt, Radian

Corporation, to Municipal Solid Waste Landfills Docket A-88-09. April 28, 1993.

Public Docket No. A-88-09.

• Methane Emissions from Landfills and Open Dumps, In EPA Report to Congress on

International Anthropogenic Methane Emissions: Estimates for 1990. S.A.

Thorneloe, M. Doorn, and M. Barlaz. EP A, Office of Policy, Planning and

Evaluation. Washington, DC, 1994. EPA-230-R-93-010.

• Landfill Gas Utilization – Options, Benefits, and Barriers, The Second United States

Conference on Municipal Solid Waste Management, Arlington, VA. S.A. Thorneloe.

Published in Conference Proceedings, June 3S5, 1992.

• Global Methane Emissions from Waste Management. S.A. Thorneloe, M. A. Barlaz,

R. Peer, L. C. Huff, L. Davis, and J. Mangino. Published in Atmospheric Methane:

Sources, Sinks, and Role in Global Change, NATO ASI Series, Vol. 13, 1993.

References

EPA, 1991a. Air Emissions from Municipal Solid Waste Landfills. Background Information

for Proposed Standards and Guidelines, EPA-450/3-90-011a (NTIS PB91-197061), U.S.

Environmental Protection Agency, Research Triangle Park, NC.
39

EPA, 1991b. Standards of Performance for New Stationary Sources and Guidelines for

Control of Existing Sources: Municipal Solid Waste Landfills, proposed rule. Federal

Register, 56 FR 24468, May 30.

EPA, 1991c. Regulatory Package for New Source Performance Standards and III(d)

Guidelines for Municipal Solid Waste Air Emissions, Public Docket No. A-88-09 (proposed

May 1991). U.S. Environmental Protection Agency, Research Triangle Park, NC.

EPA, 1996. Standards of Performance for New Stationary Sources and Guidelines for

Control of Existing Sources: Municipal Solid Waste Landfills, final rule. Federal Register,

61 FR 9905, March 12.

EPA, 1998. Compilation of Air Pollutant Emission Factors, AP-42, Volume 1: Stationary

Point and Area Sources, 5th ed., Supplement E, Chapter 2.4: Municipal Solid Waste

Landfills. U.S. Environmental Protection Agency, Office of Air Quality Planning and

Standards, Research Triangle Park, NC, November.

McGuinn, Y.C., 1988a. Memorandum. Radian Corporation, to Susan Thorneloe, EPA. Use

of Landfill Gas Generation Model to Estimate VOC Emissions from Landfills, Public Docket

No. A-88-09, June 21.

McGuinn, Y.C., 1988b. Memorandum. Radian Corporation, to Susan Thorneloe, EPA.

Sensitivity Analysis of Landfill Gas Generation Model, Public Docket

No. A-88-09, June 21.

National Archives and Records Administration (NARA), 1997a. Code of Federal

Regulations, Part 60, Protection of the Environment, Subpart WWW - Standards of

Performance for Municipal Solid Waste Landfills, Office of the Federal Register,

Washington, DC.

NARA, 1997b. Code of Federal Regulations, Part 60, Protection of the Environment,

Subpart Cc - Emission Guidelines and Compliance Times for Municipal Solid Waste

Landfills, Office of the Federal Register, Washington, DC.

Pelt, W.R., 1993. Memorandum. Radian Corporation to Municipal Solid Waste Landfills

Docket A-88-09, Methodology Used to Revise the Model Inputs in the Municipal Solid

Waste Landfills Input Database (Revised), Public Docket No. A-88-09, April 28.
40

Thorneloe, S.A., A. Reisdorph, M. Laur, R. Pelt, R.L. Bass, and C. Burklin, 1999. The U.S.

Environmental Protection Agency’s Landfill Gas Emissions Model (LandGEM), Sardinia

99, Seventh International Waste Management and Landfill Symposium, Published in

Proceedings, Volume IV, Pages 11S18, October 4S8.

Thorneloe, S.A. and J.G. Pacey, 1994. Landfill Gas Utilization--Database of North

American Projects, Presented at the 17th Annual International Landfill Gas Symposium by

the Solid Waste Association of North America, Long Beach, CA, March 22-24.

Thorneloe, S.A., M. Doorn, M. Barlaz, et al., 1994. Methane Emissions from Landfills and

Open Dumps, In EPA Report to Congress on International Anthropogenic Methane

Emissions: Estimates for 1990. EPA-230-R-93-010.
41

Appendix A

Technical Background
42

Introduction

The Landfill Gas Emissions Model (LandGEM) provides an automated estimation tool

for quantifying air emissions from municipal solid waste (MSW) landfills. The model was

developed by the Control Technology Center (CTC) of the U.S. Environmental Protection

Agency and can be obtained by downloading from the TTNWeb

(http://www.epa.gov/ttn/catc/products.html#software). It is also available from the National

Technical Information Service (NTIS).

Air emissions from landfills come from landfill gas generated by the decomposition of waste

in the landfill. Landfill gas is assumed by this model to be roughly half methane and half

carbon dioxide with additional, relatively low, concentrations of other air pollutants. The

following information is needed to estimate emissions from a landfill (see the Glossary of

Terms at the end of Appendix A):

• The waste design capacity of the landfill,

• The amount of waste-in-place in the landfill or the annual waste acceptance rate for

the landfill,

• The methane generation rate (k),

• The potential methane generation capacity (Lo),

• The concentration of total nonmethane organic compounds (NMOCs) and speciated

NMOCs found in the landfill gas,

• The years the landfill has been in operation, and

• Whether the landfill has been used for disposal of hazardous waste (co-disposal).

The estimation method used by the model is a simple first-order decay equation. Because

the data available for landfills (such as data on the quantity, age, and composition of the

waste in the landfill) are limited, using a more sophisticated calculation method is not

justified. The Landfill Gas Emissions Model estimates emissions of total landfill gas,

methane, carbon dioxide (CO2), NMOCs, and selected air pollutants. Information on the

assumptions used in the model can be found in the background information document (EPA,

1991a) written to support the Standards of Performance for New Stationary Sources

(NARA, 1997a) and Emission Guidelines for Control of Existing Sources (NARA, 1997b)

and in the public docket (McGuinn, 1988a; McGuinn, 1988b; Pelt, 1993).

The Landfill Gas Emissions Model can be used with site-specific data for all the information

needed to generate emission estimates, or it can be used with two different sets of default

values. One set of default values (the CAA defaults) is for estimating emissions to determine

the applicability of the Clean Air Act (CAA) regulations for MSW landfill emissions,
43

specifically the New Source Performance Standards (NSPS) for new MSW Landfills and the

emission guidelines (EG) for existing MSW landfills. The NSPS/EG were initially proposed

May 30, 1991 (EPA, 1991b), and the final rule was promulgated on March 12, 1996

(EPA, 1996).

The applicability of the NSPS/EG to a particular landfill can be determined based on

emissions estimated using the CAA defaults in the model. The applicability of the NSPS/EG

to a particular landfill is determined in tiers. There is, first, a size cutoff (i.e., 2.5 million

tons or 2.5 million cubic meters of waste) below which landfills are not subject to the rule.

After the size cutoff, the first tier of the applicability determination is to assess whether

emissions of NMOCs exceed a cutoff value of 50 Mg of NMOCs/yr using LandGEM with

all default values set for the CAA defaults. Landfills with emissions exceeding the cutoff

value can choose to install emission controls or move to the second tier of the applicability

determination, which is to test the landfill for landfill gas NMOC concentrations. If the

revised NMOC concentrations result in NMOC emissions that still exceed the cutoff value,

the landfill can choose to install emission controls or move to the third tier of the

applicability determination, which is to perform another test to obtain a site-specific k value

(the methane generation rate constant).

The CAA default values in the model provide emission estimates that would reflect the

expected maximum emissions and generally would be used only for determining the

applicability of the regulations to a landfill. To estimate actual emissions in the absence of

site-specific data, a second set of default values (the inventory defaults) is provided in the

model. The inventory default values in the model are based on emission factors from the

U.S. Environmental Protection Agency’s Compilation of Air Pollutant Emission Factors,

AP-42 (EPA, 1998). The inventory default values provide emission estimates that should

reflect typical landfill emissions and are the values suggested for use in developing

estimates for state inventories.

The EPA fully recognizes that modeling landfill air emissions 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. As better data become available, including longer term data on landfill air

emissions, better modeling approaches are expected to evolve. For example, several firms in

the landfill gas industry have models for estimating landfill emissions that are regarded as

proprietary. If this information is released to the public, the EPA can use it to improve the

present emission estimation approach. In addition, as data become available through the
44

implementation of the NSPS/EG, the new data can be used to improve the modeling

calculations.

Landfill Emissions

The Landfill Gas Emissions Model estimates the emissions resulting from the

biodegradation of waste in landfills. The anaerobic decomposition of waste in MSW

landfills causes emissions of landfill gas. As landfill gas passes through the waste, it sweeps

NMOCs and other air pollutants present in the waste to the surface. The composition of

MSW landfill emissions is estimated by the model to be about 50 percent methane (CH4)

and 50 percent carbon dioxide (CO2), with additional, trace constituents of NMOCs,

although, these default percentages can easily be changed. The concentration of total and

speciated NMOCs can be estimated by the model using either default or site-specific

concentrations. The pollutant regulated under the NSPS/EG is MSW landfill emissions, but

the surrogate for measuring MSW landfill emissions for the applicability of and compliance

with the regulations is NMOCs.

The EPA has determined that emissions from MSW landfills cause, or contribute

significantly to, air pollution that may reasonably be anticipated to endanger public health or

welfare. Some NMOCs are known or suspected carcinogens, or cause other noncancer

health effects. Public welfare concerns include the odor nuisance from the landfill gas and

the potential for CH4 migration, both on-site and off-site, which may lead to explosions or

fires. The CH4 emitted from landfills is also a concern because it is a greenhouse gas and

contributes to global climate change. It has been estimated that the United States contributed

8 to 16 Tg/yr of CH4 to the atmosphere in 1990, about 40 percent of the worldwide amount

emitted from landfills and open dumps (Thorneloe and Pacey, 1994; Thorneloe et al., 1994).

The environmental and welfare concerns associated with MSW landfill air emissions are

documented in the preamble to the proposed NSPS/EG (EPA, 1991c).

This computer model uses a first-order decomposition rate equation and estimates annual

emissions over any time period specified by the user. Total landfill gas emissions are

estimated by estimating CH4 generation and doubling it (the landfill gas is assumed to be

half CH4 and half CO2). Methane generation is estimated using Lo, the potential CH4

generation capacity of the waste, and k, the CH4 generation rate constant, which accounts for

how quickly the CH4 generation rate decreases once it reaches its peak rate. The CH4

generation rate is assumed to be at its peak upon closure of the landfill or final placement of

waste at the site. The model allows the user to enter Lo and k values derived using sitespecific test data collected at the landfill (site-specific data may be collected using the test
45

methods specified in the NSPS/EG for MSW landfills), or to use the CAA or inventory

default values.

The model estimates emission rates for total landfill gas, CH4, CO2, NMOCs, and a list of air

pollutants expected to be emitted from landfills based on test data from AP-42 (EPA, 1998).

Methane and Carbon Dioxide

The NSPS/EG require only NMOC emission estimates, but the model provides estimates of

all landfill gas constituents. Landfill gas is assumed to be half CH4 and half CO2. The model

assumes that CO2 emissions are the same as CH4 emissions and that landfill gas emissions

are twice the CH4 emissions. The generation of CH4 from a landfill is a function of k, the

CH4 generation rate constant, and Lo, the CH4 generation potential.

The CH4 generation rate constant, k, determines the rate of CH4 generation for each submass

of waste in the landfill. The higher the value of k, the faster the CH4 generation rate

increases and then decays over time. The value of k is a function of (1) waste moisture

content, (2) availability of the nutrients for methanogens, (3) pH, and (4) temperature. The k

values obtained from the data collected for the NSPS/EG range from 0.003 to 0.21 (EPA,

1991a). These values were obtained from theoretical models using field test data and from

actual field test measurements. If no user-specified k value is entered into LandGEM, a

default value is used. The default k value used by the model is 0.05 year-1 for the CAA

conventional landfills option (EPA, 1991a).

The value for the potential CH4 generation capacity of waste (Lo) depends only on the type

of waste in the landfill. The higher the cellulose content of the waste, the higher the value of

Lo. The values of theoretical and obtainable Lo range from 6.2 to 270 m3

/Mg of waste (EPA,

1991c). If no user-specified Lo value is entered into LandGEM, a default value is used for

Lo. The default Lo value used in the model is 170 m3

/Mg of waste for the CAA conventional

landfills option (EPA, 1991a).

Air Pollutants

Landfill gas contains low concentrations of air pollutants from the leaching and

decomposition of waste. The Landfill Gas Emissions Model can estimate emissions of such

air pollutants if users choose to do so. Emissions of air pollutants are based on

concentrations of air pollutants in the landfill gas. The model contains default concentrations

for specific air pollutant compounds. The list of air pollutants expected to be emitted with
46

landfill gas and the concentrations of these air pollutants were taken from test data in AP-42

(EPA, 1998). The default air pollutants included in the model are designated as a hazardous

air pollutant (HAP) or a volatile organic compound (VOC) with the HAP or VOC

abbreviation after their chemical names. These designations are based on EPA HAP and

VOC definitions that are current as of April 2004.

Because some air pollutant concentrations in the landfill gas are slightly higher for landfills

that have been used for disposal of hazardous waste than for those that have not, there is a

choice in the model between “Co-disposal,” (i.e., landfills used for disposal of hazardous

and non-hazardous waste), and “No or Unknown Co-disposal,” (i.e., landfills that have not

been used for disposal of hazardous waste or unknown disposal of hazardous waste). For

example, concentrations in the model for benzene and toluene are different for landfills with

hazardous waste “Co-disposal” than for landfills with “No or Unknown Codisposal.”

Landfill sites that have hazardous waste co-disposal or Superfund sites should use the codisposal option for estimating air pollutant emissions. In general, it is recommended that

landfill owners and operators obtain actual test data for air pollutant concentrations in the

landfill gas for their specific landfill.

Nonmethane Organic Compounds

The NMOC concentration in the landfill gas is a function of the types of waste in the landfill

and the extent of the reactions that produce various compounds from the anaerobic

decomposition of waste. To determine NMOC concentrations, NMOC data were collected

from emission test reports from industry, state, and local regulatory agencies (Pelt, 1993).

The NMOC concentrations from 23 landfills ranged from 240 to 14,300 ppmv. Three

suggested default NMOC concentrations are used in the model: one for the CAA default

option and two for the inventory default option (one for co-disposal and one for no or

unknown co-disposal). For the CAA default option, the NMOC concentration as hexane is

4,000 ppmv. For the inventory default option, the NMOC concentration as hexane for

co-disposal is 2,400 ppmv and is 600 ppmv for no or unknown co-disposal. The analysis of

NMOC concentrations in landfill gas is documented in a memorandum (Pelt, 1993), which

can be found in Public Docket No. A-88-09 and in AP-42 (EPA, 1998). Because the NMOC

concentration in landfill gas varies from landfill to landfill, collection of site-specific data

using EPA Method 25C will provide the most accurate estimates (EPA, 1991c).
47

GLOSSARY OF TERMS

Term Definition

Co-disposal Disposal of hazardous waste as well as other

kinds of waste in a landfill.

Waste Design Capacity The total amount of waste that can be

disposed of in the landfill.

Landfill Gas Landfill gas is a product of biodegradation of

waste in landfills and consists of primarily

CH4 and CO2, with trace amounts of NMOCs

and air pollutants.

Methane Generation Rate (k) k is a constant that determines the rate of

landfill gas generation. The first-order

decomposition rate assumes that k values

before and after peak landfill gas generation

are the same. k is a function of moisture

content in the landfill waste, availability of

nutrients for methanogens, pH, and

temperature.

Nonmethane Organic Compounds

(NMOCs)

NMOCs are specified in this program as the

fraction of landfill gas containing

nonmethane organic compounds, expressed

as hexane. NMOCs include air pollutants and

VOCs. NMOC concentration can be

measured using guidance provided by EPA

Method 25C.

Potential Methane Generation Capacity

(Lo)

Lo is a constant that represents the potential

capacity of a landfill to generate CH4 (a

primary constituent of landfill gas). Lo

depends on the amount of cellulose in the

waste.

Air Pollutants Compounds found in landfill gas or emitted

with landfill gas, some of which are listed as

air pollutants under section 112 of the Clean

Air Act (CAA). A total of 46 air pollutants

emitted from landfills are included in the

model.

Landfill Closure Year The year in which the landfill ceases, or is 

expected to cease, accepting waste.
48

Eastern Research Group

Morrisville, NC

3C-R127-NALX

TECHNICAL REPORT DATA

(Please read Instructions on the reverse before completing)

1. REPORT NO. 2. 3. RECIPIENT'S ACCESSION NO.

EPA-600/R-05/047

4. TITLE AND SUBTITLE 5. REPORT DATE

Landfill Gas Emissions Model (LandGEM) Version 3.02 User’s

Guide

 May 2005

6. PERFORMING ORGANIZATION CODE

7. AUTHORS 8. PERFORMING ORGANIZATION REPORT NO.

Amy Alexander, Clint Burklin, and Amanda Singleton (ERG)

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO.

11. CONTRACT/GRANT NO.

12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED

U. S. EPA, Office of Research and Development

Air Pollution Prevention and Control Division

Research Triangle Park, North Carolina 27711

Software User’s Guide; 4/28/03S4/28/04

14. SPONSORING AGENCY CODE

EPA/600/13

15. SUPPLEMENTARY NOTES

The EPA Project Officer is Susan A. Thorneloe, mail drop E305-02, phone (919) 541-2709, e-mail

Thorneloe.Susan@epamail.epa.gov

16. ABSTRACT

The Landfill Gas Emissions Model (LandGEM) is an automated estimation tool with a Microsoft Excel

interface that can be used to estimate emission rates for total landfill gas, methane, carbon dioxide,

nonmethane organic compounds, and individual air pollutants from municipal solid waste landfills. This

guide provides step-by-step guidance for using this software application, as well as an appendix containing

background information on the technical basis of LandGEM. LandGEM can use either site-specific data to

estimate emissions or default parameters if no site-specific data are available. The model contains two sets

of default parameters, CAA defaults and inventory defaults. The CAA defaults are based on federal

regulations for MSW landfills laid out by the Clean Air Act (CAA) and can be used for determining whether a

landfill is subject to the control requirements of these regulations. The inventory defaults are based on

emission factors in EPA’s Compilation of Air Pollutant Emission Factors (AP-42) and can be used to

generate emission estimates for use in emission inventories and air permits in the absence of site-specific

test data.

17. KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS b. IDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group

Air Pollution

Landfills

Mathematical Models

Computer Simulation

Methane

Carbon Dioxide

Emission

Pollution Control

Stationary Sources

13B

13C

12A

14B

07C

07B

14G

18. DISTRIBUTION STATEMENT 19. SECURITY CLASS (This Report) 21. NO. OF PAGES

Release to Public

 Unclassified 54

20. SECURITY CLASS (This Page) 22. PRICE

 Unclassified

 EPA Form 2220-1 (Rev. 4-77 ) PREVIOUS EDITION IS OBSOLETE