11/98 Solid Waste Disposal 2.4-1

2.4 MUNICIPAL SOLID WASTE LANDFILLS

2.4.1 General1-4

A municipal solid waste (MSW) landfill unit is a discrete area of land or an excavation that receives

household waste, and that is not a land application unit, surface impoundment, injection well, or waste pile. 

An MSW landfill unit may also receive other types of wastes, such as commercial solid waste, nonhazardous

sludge, and industrial solid waste. The municipal solid waste types potentially accepted by MSW landfills

include (most landfills accept only a few of the following categories):

• MSW,

• Household hazardous waste,

• Municipal sludge,

• Municipal waste combustion ash,

• Infectious waste,

• Waste tires,

• Industrial non-hazardous waste,

• Conditionally exempt small quantity generator (CESQG) hazardous waste,

• Construction and demolition waste,

• Agricultural wastes,

• Oil and gas wastes, and

• Mining wastes.

In the United States, approximately 57 percent of solid waste is landfilled, 16 percent is incinerated, and

27 percent is recycled or composted. There were an estimated 2,500 active MSW landfills in the United

States in 1995. These landfills were estimated to receive 189 million megagrams (Mg) (208 million tons) of

waste annually, with 55 to 60 percent reported as household waste, and 35 to 45 percent reported as

commercial waste.

2.4.2 Process Description2,5

There are three major designs for municipal landfills. These are the area, trench, and ramp methods. All

of these methods utilize a three step process, which includes spreading the waste, compacting the waste, and

covering the waste with soil. The trench and ramp methods are not commonly used, and are not the preferred

methods when liners and leachate collection systems are utilized or required by law. The area fill method

involves placing waste on the ground surface or landfill liner, spreading it in layers, and compacting with

heavy equipment. A daily soil cover is spread over the compacted waste. The trench method entails

excavating trenches designed to receive a day's worth of waste. The soil from the excavation is often used for

cover material and wind breaks. The ramp method is typically employed on sloping land, where waste is

spread and compacted similar to the area method, however, the cover material obtained is generally from the

front of the working face of the filling operation.

Modern landfill design often incorporates liners constructed of soil (i.e., recompacted clay), or synthetics

(i.e., high density polyethylene), or both to provide an impermeable barrier to leachate (i.e., water that has

passed through the landfill) and gas migration from the landfill.
2.4-2 EMISSION FACTORS 11/98

2.4.3 Control Technology1,2,6

The Resource Conservation and Recovery Act (RCRA) Subtitle D regulations promulgated on

October 9, 1991 require that the concentration of methane generated by MSW landfills not exceed 25 percent

of the lower explosive limit (LEL) in on-site structures, such as scale houses, or the LEL at the facility

property boundary.

The New Source Performance Standards (NSPS) and Emission Guidelines for air emissions from MSW

landfills for certain new and existing landfills were published in the Federal Register on March 1, 1996. The

regulation requires that Best Demonstrated Technology (BDT) be used to reduce MSW landfill emissions

from affected new and existing MSW landfills emitting greater than or equal to 50 Mg/yr (55 tons/yr) of nonmethane organic compounds (NMOCs). The MSW landfills that are affected by the NSPS/Emission

Guidelines are each new MSW landfill, and each existing MSW landfill that has accepted waste since

November 8, 1987, or that has capacity available for future use. The NSPS/Emission Guidelines affect

landfills with a design capacity of 2.5 million Mg (2.75 million tons) or more. Control systems require: (1) a

well-designed and well-operated gas collection system, and (2) a control device capable of reducing NMOCs

in the collected gas by 98 weight-percent.

Landfill gas (LFG) collection systems are either active or passive systems. Active collection systems

provide a pressure gradient in order to extract LFG by use of mechanical blowers or compressors. Passive

systems allow the natural pressure gradient created by the increase in pressure created by LFG generation

within the landfill to mobilize the gas for collection.

LFG control and treatment options include (1) combustion of the LFG, and (2) purification of the LFG. 

Combustion techniques include techniques that do not recover energy (i.e., flares and thermal incinerators),

and techniques that recover energy (i.e., gas turbines and internal combustion engines) and generate electricity

from the combustion of the LFG. Boilers can also be employed to recover energy from LFG in the form of

steam. Flares involve an open combustion process that requires oxygen for combustion, and can be open or

enclosed. Thermal incinerators heat an organic chemical to a high enough temperature in the presence of

sufficient oxygen to oxidize the chemical to carbon dioxide (CO ) and water. Purification techniques can 2

also be used to process raw landfill gas to pipeline quality natural gas by using adsorption, absorption, and

membranes.

2.4.4 Emissions2,7

Methane (CH ) and CO are the primary constituents of landfill gas, and are produced by 4 2

microorganisms within the landfill under anaerobic conditions. Transformations of CH and CO are 4 2

mediated by microbial populations that are adapted to the cycling of materials in anaerobic environments. 

Landfill gas generation, including rate and composition, proceeds through four phases. The first phase is

aerobic [i.e., with oxygen (O ) available] and the primary gas produced is CO . The second phase is 2 2

characterized by O depletion, resulting in an anaerobic environment, where large amounts of CO and some 2 2

hydrogen (H ) are produced. In the third phase, CH production begins, with an accompanying reduction in 2 4

the amount of CO produced. Nitrogen (N ) content is initially high in landfill gas in the first phase, and 2 2

declines sharply as the landfill proceeds through the second and third phases. In the fourth phase, gas

production of CH , CO , and N becomes fairly steady. The total time and phase duration of gas generation 4 2 2

varies with landfill conditions (i.e., waste composition, design management, and anaerobic state).

Typically, LFG also contains a small amount of non-methane organic compounds (NMOC). This

NMOC fraction often contains various organic hazardous air pollutants (HAP), greenhouse gases (GHG),

and compounds associated with stratospheric ozone depletion. The NMOC fraction also contains volatile
QCH4

' Lo R (e &kc & e &kt)

1/98 Solid Waste Disposal 2.4-3

(1)

organic compounds (VOC). The weight fraction of VOC can be determined by subtracting the weight

fractions of individual compounds that are non-photochemically reactive (i.e., negligibly-reactive organic

compounds as defined in 40 CFR 51.100).

Other emissions associated with MSW landfills include combustion products from LFG control and

utilization equipment (i.e., flares, engines, turbines, and boilers). These include carbon monoxide (CO),

oxides of nitrogen (NO ), sulfur dioxide (SO ), hydrogen chloride (HCl), particulate matter (PM) and other x 2

combustion products (including HAPs). PM emissions can also be generated in the form of fugitive dust

created by mobile sources (i.e., garbage trucks) traveling along paved and unpaved surfaces. The reader

should consult AP-42 Volume I Sections 13.2.1 and 13.2.2 for information on estimating fugitive dust

emissions from paved and unpaved roads.

The rate of emissions from a landfill is governed by gas production and transport mechanisms. 

Production mechanisms involve the production of the emission constituent in its vapor phase through

vaporization, biological decomposition, or chemical reaction. Transport mechanisms involve the

transportation of a volatile constituent in its vapor phase to the surface of the landfill, through the air

boundary layer above the landfill, and into the atmosphere. The three major transport mechanisms that

enable transport of a volatile constituent in its vapor phase are diffusion, convection, and displacement.

2.4.4.1 Uncontrolled Emissions — To estimate uncontrolled emissions of the various compounds present in

landfill gas, total landfill gas emissions must first be estimated. Uncontrolled CH emissions may be 4

estimated for individual landfills by using a theoretical first-order kinetic model of methane production

developed by the EPA. This model is known as the Landfill Air Emissions Estimation model, and can be 8

accessed from the Office of Air Quality Planning and Standards Technology Transfer Network Website

(OAQPS TTN Web) in the Clearinghouse for Inventories and Emission Factors (CHIEF) technical area

(URL http://www.epa.gov/ttn/chief). The Landfill Air Emissions Estimation model equation is as follows:

where:

 Q = Methane generation rate at time t, m /yr; CH 4

3

L = Methane generation potential, m CH /Mg refuse; o

3

4

R = Average annual refuse acceptance rate during active life, Mg/yr;

e = Base log, unitless;

k = Methane generation rate constant, yr ; -1

c = Time since landfill closure, yrs (c = 0 for active landfills); and

t = Time since the initial refuse placement, yrs.

It should be noted that the model above was designed to estimate LFG generation and not LFG emissions

to the atmosphere. Other fates may exist for the gas generated in a landfill, including capture and subsequent

microbial degradation within the landfill’s surface layer. Currently, there are no data that adequately address

this fate. It is generally accepted that the bulk of the gas generated will be emitted through cracks or other

openings in the landfill surface.

Site-specific landfill information is generally available for variables R, c, and t. When refuse acceptance

rate information is scant or unknown, R can be determined by dividing the refuse in place by the age of the

landfill. If a facility has documentation that a certain segment (cell) of a landfill received only nondegradable

refuse, then the waste from this segment of the landfill can be excluded from the calculation of R. 

Nondegradable refuse includes concrete, brick, stone, glass, plaster, wallboard, piping, plastics, and metal
2.4-4 EMISSION FACTORS 11/98

objects. The average annual acceptance rate should only be estimated by this method when there is

inadequate information available on the actual average acceptance rate. The time variable, t, includes the

total number of years that the refuse has been in place (including the number of years that the landfill has

accepted waste and, if applicable, has been closed). 

Values for variables L and k must be estimated. Estimation of the potential CH generation capacity of o 4

refuse (L ) is generally treated as a function of the moisture and organic content of the refuse. Estimation of o

the CH generation constant (k) is a function of a variety of factors, including moisture, pH, temperature, and 4

other environmental factors, and landfill operating conditions. Specific CH generation constants can be 4

computed by the use of EPA Method 2E (40 CFR Part 60 Appendix A).

The Landfill Air Emission Estimation model includes both regulatory default values and recommended

AP-42 default values for L and k. The regulatory defaults were developed for compliance purposes o

(NSPS/Emission Guideline). As a result, the model contains conservative L and k default values in order to o

protect human health, to encompass a wide range of landfills, and to encourage the use of site-specific data. 

Therefore, different L and k values may be appropriate in estimating landfill emissions for particular o

landfills and for use in an emissions inventory.

Recommended AP-42 defaults include a k value of 0.04/yr for areas recieving 25 inches or more of rain

per year. A default k of 0.02/yr should be used in drier areas (<25 inches/yr). An L value of 100 m /Mg o 3

(3,530 ft /ton) refuse is appropriate for most landfills. Although the recommended default k and L are 3 o

based upon the best fit to 21 different landfills, the predicted methane emissions ranged from 38 to 492% of

actual, and had a relative standard deviation of 0.85. It should be emphasized that in order to comply with the

NSPS/Emission Guideline, the regulatory defaults for k and L must be applied as specified in the final rule. o

When gas generation reaches steady state conditions, LFG consists of approximately 40 percent by

volume CO , 55 percent CH , 5 percent N (and other gases), and trace amounts of NMOCs. Therefore, the 2 4 2

estimate derived for CH generation using the Landfill Air Emissions Estimation model can also be used to 4

represent CO generation. Addition of the CH and CO emissions will yield an estimate of total landfill gas 2 4 2

emissions. If site-specific information is available to suggest that the CH content of landfill gas is not 4

55 percent, then the site-specific information should be used, and the CO emission estimate should be 2

adjusted accordingly.

Most of the NMOC emissions result from the volatilization of organic compounds contained in the

landfilled waste. Small amounts may be created by biological processes and chemical reactions within the

landfill. The current version of the Landfill Air Emissions Estimation model contains a proposed regulatory

default value for total NMOC of 4,000 ppmv, expressed as hexane. However, available data show that there

is a range of over 4,400 ppmv for total NMOC values from landfills. The proposed regulatory default value

for NMOC concentration was developed for regulatory compliance purposes and to provide the most

cost-effective default values on a national basis. For emissions inventory purposes, site-specific information

should be taken into account when determining the total NMOC concentration. In the absence of site-specific

information, a value of 2,420 ppmv as hexane is suggested for landfills known to have co-disposal of MSW

and non-residential waste. If the landfill is known to contain only MSW or have very little organic

commercial/industrial wastes, then a total NMOC value of 595 ppmv as hexane should be used. In addition,

as with the landfill model defaults, the regulatory default value for NMOC content must be used in order to

comply with the NSPS/Emission Guideline.

If a site-specific total pollutant concentration is available (i.e., as measured by EPA Reference Method

25C), it must be corrected for air infiltration which can occur by two different mechanisms: LFG sample

dilution, and air intrusion into the landfill. These corrections require site-specific data for the LFG CH , 4
CP (ppmv) (corrected for air infiltration) ' CP (ppmv) (1 x 106

)

CCO2

(ppmv) % CCH4(ppmv)

QP ' 1.82 QCH4

(

CP

(1 x 106)

UMP ' QP (

MWP ( 1 atm

(8.205x10&5 m3&atm/gmol&EK)(1000g/kg)(273%T EK)

11/98 Solid Waste Disposal 2.4-5

(2)

(3)

(4)

CO , nitrogen (N ), and oxygen (O ) content. If the ratio of N to O is less than or equal to 4.0 (as found in 2 2 2 2 2

ambient air), then the total pollutant concentration is adjusted for sample dilution by assuming that CO and 2

CH are the primary (100 percent) constituents of landfill gas, and the following equation is used: 4

where:

C = Concentration of pollutant P in landfill gas (i.e., NMOC as hexane), ppmv; P 

 C = CO concentration in landfill gas, ppmv CO 2 2 ;

 C = CH Concentration in landfill gas, ppmv; and CH 4 4

 1 x 10 = Constant used to correct concentration of P to units of ppmv. 6

If the ratio of N to O concentrations (i.e., C , C ) is greater than 4.0, then the total pollutant 2 2 N 2 2 O 

concentration should be adjusted for air intrusion into the landfill by using equation 2 and adding the

concentration of N (i.e., C ) to the denominator. Values for C O , C H , C , C , can usually be 2 N 2 2 4 2 2 C C N O 

found in the source test report for the particular landfill along with the total pollutant concentration data.

To estimate emissions of NMOC or other landfill gas constituents, the following equation should be

used:

where:

 Q = Emission rate of pollutant P (i.e. NMOC), m /yr; P 3

 Q = CH generation rate, m /yr (from the Landfill Air Emissions Estimation model); CH 4 4

3

 C = Concentration of P in landfill gas, ppmv; and P

 1.82 = Multiplication factor (assumes that approximately 55 percent of landfill gas is CH4

and 45 percent is CO , N , and other constituents). 2 2

 Uncontrolled mass emissions per year of total NMOC (as hexane), CO , CH , and speciated organic and 2 4

inorganic compounds can be estimated by the following equation:

where:

 UM = Uncontrolled mass emissions of pollutant P (i.e., NMOC), kg/yr; P

 MW = Molecular weight of P, g/gmol (i.e., 86.18 for NMOC as hexane); P

 Q = NMOC emission rate of P, m /yr; and P 3

 T = Temperature of landfill gas, C. o

This equation assumes that the operating pressure of the system is approximately 1 atmosphere. If the

temperature of the landfill gas is not known, a temperature of 25 C (77 F) is recommended. o o
CMP ' UMP ( 1 & 0col

100 % UMP (

0col

100

( 1 & 0cnt

100

2.4-6 EMISSION FACTORS 11/98

(5)

Uncontrolled default concentrations of speciated organics along with some inorganic compounds are

presented in Table 2.4-1. These default concentrations have already been corrected for air infiltration and can

be used as input parameters to equation 3 or the Landfill Air Emission Estimation model for estimating 

speciated emissions from landfills when site-specific data are not available. An analysis of the data, based on

the co-disposal history (with non-residential wastes) of the individual landfills from which the concentration

data were derived, indicates that for benzene, NMOC, and toluene, there is a difference in the uncontrolled

concentrations. Table 2.4-2 presents the corrected concentrations for benzene, NMOC, and toluene to use

based on the site's co-disposal history.

It is important to note that the compounds listed in Tables 2.4-1 and 2.4-2 are not the only compounds

likely to be present in LFG. The listed compounds are those that were identified through a review of the

available literature. The reader should be aware that additional compounds are likely present, such as those

associated with consumer or industrial products. Given this information, extreme caution should be exercised

in the use of the default VOC weight fractions and concentrations given at the bottom of Table 2.4-2. These

default VOC values are heavily influenced by the ethane content of the LFG. Available data have shown that

there is a range of over 1,500 ppmv in LFG ethane content among landfills.

2.4.4.2 Controlled Emissions — Emissions from landfills are typically controlled by installing a gas

collection system, and combusting the collected gas through the use of internal combustion engines, flares, or

turbines. Gas collection systems are not 100 percent efficient in collecting landfill gas, so emissions of CH4

and NMOC at a landfill with a gas recovery system still occur. To estimate controlled emissions of CH , 4

NMOC, and other constituents in landfill gas, the collection efficiency of the system must first be estimated. 

Reported collection efficiencies typically range from 60 to 85 percent, with an average of 75 percent most

commonly assumed. Higher collection efficiencies may be achieved at some sites (i.e., those engineered to

control gas emissions). If site-specific collection efficiencies are available (i.e., through a comprehensive

surface sampling program), then they should be used instead of the 75 percent average. 

Controlled emission estimates also need to take into account the control efficiency of the control device. 

Control efficiencies based on test data for the combustion of CH , NMOC, and some speciated organics with 4

differing control devices are presented in Table 2.4-3. Emissions from the control devices need to be added

to the uncollected emissions to estimate total controlled emissions. 

Controlled CH , NMOC, and speciated emissions can be calculated with equation 5. It is assumed that 4

the landfill gas collection and control system operates 100 percent of the time. Minor durations of system

downtime associated with routine maintenance and repair (i.e., 5 to 7 percent) will not appreciably effect

emission estimates. The first term in equation 5 accounts for emissions from uncollected landfill gas, while

the second term accounts for emissions of the pollutant that were collected but not combusted in the control

or utilization device:

where:

CM = Controlled mass emissions of pollutant P, kg/yr; P

UM = Uncontrolled mass emissions of P, kg/yr (from equation 4 or the Landfill Air P

Emissions Estimation Model);

 0 = Collection efficiency of the landfill gas collection system, percent; and col

0 = Control efficiency of the landfill gas control or utilization device, percent. cnt
CMCO2

' UMCO2% UMCH4(

0col

100

( 2.75

CMSO2

' UMS (

0col

100

( 2.0

11/98 Solid Waste Disposal 2.4-7

(6)

(7)

Emission factors for the secondary compounds, CO and NO , exiting the control device are x

presented in Tables 2.4-4 and 2.4-5. These emission factors should be used when equipment vendor

guarantees are not available.

Controlled emissions of CO and sulfur dioxide (SO ) are best estimated using site-specific landfill gas 2 2

constituent concentrations and mass balance methods. If site-specific data are not available, the data in 68 

tables 2.4-1 through 2.4-3 can be used with the mass balance methods that follow. 

Controlled CO emissions include emissions from the CO component of landfill gas (equivalent to 2 2

uncontrolled emissions) and additional CO formed during the combustion of landfill gas. The bulk of the 2

CO formed during landfill gas combustion comes from the combustion of the CH fraction. Small quantities 2 4

will be formed during the combustion of the NMOC fraction, however, this typically amounts to less than 1

percent of total CO emissions by weight. Also, the formation of CO through incomplete combustion of 2

landfill gas will result in small quantities of CO not being formed. This contribution to the overall mass 2

balance picture is also very small and does not have a significant impact on overall CO emissions. 2

68

The following equation which assumes a 100 percent combustion efficiency for CH can be used to 4

estimate CO emissions from controlled landfills: 2

where:

CM = Controlled mass emissions of CO , kg/yr; CO 2 2

UM = Uncontrolled mass emissions of CO , kg/yr (from equation 4 or the Landfill Air CO 2 2

Emission Estimation Model);

UM = Uncontrolled mass emissions of CH , kg/yr (from equation 4 on the Landfill Air CH 4 4

Emission Estimation Model);

0 = Efficiency of the landfill gas collection system, percent; and col

2.75 = Ratio of the molecular weight of CO to the molecular weight of CH . 2 4

To prepare estimates of SO emissions, data on the concentration of reduced sulfur compounds within 2

the landfill gas are needed. The best way to prepare this estimate is with site-specific information on the total

reduced sulfur content of the landfill gas. Often these data are expressed in ppmv as sulfur (S). Equations 3

and 4 should be used first to determine the uncontrolled mass emission rate of reduced sulfur compounds as

sulfur. Then, the following equation can be used to estimate SO emissions: 2

where: 

 CM = Controlled mass emissions of SO , kg/yr; SO 2 2

UM = Uncontrolled mass emissions of reduced sulfur compounds as sulfur, kg/yr (from S

equations 3 and 4);

0 = Efficiency of the landfill gas collection system, percent; and col

2.0 = Ratio of the molecular weight of SO to the molecular weight of S. 2

The next best method to estimate SO concentrations, if site-specific data for total reduced sulfur 2

compounds as sulfur are not available, is to use site-specific data for speciated reduced sulfur compound

concentrations. These data can be converted to ppmv as S with equation 8. After the total reduced sulfur as

S has been obtained from equation 8, then equations 3, 4, and 7 can be used to derive SO emissions. 2
CS ' jn

i'1 CP

( SP

CCl ' jn

i'1 CP ( ClP

CMHCl ' UMCl (

0col

100

( 1.03 (

0cnt

100

2.4-8 EMISSION FACTORS 11/98

(8)

(9)

(10)

where: 

 C = Concentration of total reduced sulfur compounds, ppmv as S (for use in equation 3); S

 C = Concentration of each reduced sulfur compound, ppmv; P

 S = Number of moles of S produced from the combustion of each reduced sulfur P

compound (i.e., 1 for sulfides, 2 for disulfides); and

 n = Number of reduced sulfur compounds available for summation.

If no site-specific data are available, a value of 46.9 ppmv can be assumed for C (for use in equation 3). S

This value was obtained by using the default concentrations presented in Table 2.4-1 for reduced sulfur

compounds and equation 8. 

Hydrochloric acid [Hydrogen Chloride (HCl)] emissions are formed when chlorinated compounds in

LFG are combusted in control equipment. The best methods to estimate emissions are mass balance methods

that are analogous to those presented above for estimating SO emissions. Hence, the best source of data to 2

estimate HCl emissions is site-specific LFG data on total chloride [expressed in ppmv as the chloride ion 

(Cl )]. If these data are not available, then total chloride can be estimated from data on individual chlorinated -

species using equation 9 below. However, emission estimates may be underestimated, since not every

chlorinated compound in the LFG will be represented in the laboratory report (i.e., only those that the

analytical method specifies).

where:

 C = Concentration of total chloride, ppmv as Cl (for use in equation 3); Cl -

 C = Concentration of each chlorinated compound, ppmv; P

Cl = Number of moles of Cl produced from the combustion of each chlorinated P -

compound (i.e., 3 for 1,1,1-trichloroethane); and

 n = Number of chlorinated compounds available for summation.

After the total chloride concentration (C ) has been estimated, equations 3 and 4 should be used to Cl

determine the total uncontrolled mass emission rate of chlorinated compounds as chloride ion (UM ). This Cl

value is then used in equation 10 below to derive HCl emission estimates:

where:

 CM = Controlled mass emissions of HCl, kg/yr; HCl

 UM = Uncontrolled mass emissions of chlorinated compounds as chloride, kg/yr (from Cl

equations 3 and 4);

 0 = Efficiency of the landfill gas collection system, percent; col

 1.03 = Ratio of the molecular weight of HCl to the molecular weight of Cl ; and -

 0 = Control efficiency of the landfill gas control or utilization device, percent. cnt
11/98 Solid Waste Disposal 2.4-9

In estimating HCl emissions, it is assumed that all of the chloride ion from the combustion of chlorinated

LFG constituents is converted to HCl. If an estimate of the control efficiency, 0 , is not available, then the cnt

high end of the control efficiency range for the equipment listed in Table 9 should be used. This assumption

is recommended to assume that HCl emissions are not under-estimated.

If site-specific data on total chloride or speciated chlorinated compounds are not available, then a default

value of 42.0 ppmv can be used for C . This value was derived from the default LFG constituent Cl

concentrations presented in Table 2.4-1. As mentioned above, use of this default may produce

underestimates of HCl emissions since it is based only on those compounds for which analyses have been

performed. The constituents listed in Table 2.4-1are likely not all of the chlorinated compounds present in

LFG.

The reader is referred to Sections 11.2-1 (Unpaved Roads, SCC 50100401), and 11-2.4 (Heavy

Construction Operations) of Volume I, and Section II-7 (Construction Equipment) of Volume II, of the

AP-42 document for determination of associated fugitive dust and exhaust emissions from these emission

sources at MSW landfills.

2.4.5 Updates Since the Fifth Edition

The Fifth Edition was released in January 1995. Supplemnt D (8/98) is a major revision of the text and

recommended emission factors conained in the section. The most significant revisions to this section since

publication in the Fifth Edition are summarized below.

C The equations to calculate the CH , CO and other constituents were simplified. 4 2

C The default L and k were revised based upon an expanded base of gas generation data. 0

C The default ratio of CO to CH was revised based upon averages observed in available source test 2 4

reports.

C The default concentrations of LFG constituents were revised based upon additional data.

C Additional control efficiencies were included and existing efficiencies were revised based upon

additional emission test data.

C Revised and expanded the recommended emission factors for secondary compounds emitted from

typical control devices.

Supplement E (11/98) includes correction in equation 10 and a very minor change in the molecular weights

for 1,1,1-Trichloroethane (methyl chloroform), 1,1-Dichloroethane, 1,2-Dichloropropane and

Trichloroethylene (trichloroethene) presented in Table 2.4-1 to agree with values presented in Perry’s

Handbook.
2.4-10 EMISSION FACTORS 11/98

Table 2.4-1. DEFAULT CONCENTRATIONS FOR LFG CONSTITUENTSa

(SCC 50100402, 50300603)

Compound Molecular Weight (ppmv) Rating

Default

Concentration Emission Factor

1,1,1-Trichloroethane (methyl chloroform) 133.41 0.48 B a

1,1,2,2-Tetrachloroethane 167.85 1.11 C a

1,1-Dichloroethane (ethylidene dichloride) 98.97 2.35 B a

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

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

1,2-Dichloropropane (propylene dichloride) 112.99 0.18 D a

2-Propanol (isopropyl alcohol) 60.11 50.1 E

Acetone 58.08 7.01 B

Acrylonitrile 53.06 6.33 D a

Bromodichloromethane 163.83 3.13 C

Butane 58.12 5.03 C

Carbon disulfide 76.13 0.58 C a

Carbon monoxide 28.01 141 E b

Carbon tetrachloride 153.84 0.004 B a

Carbonyl sulfide 60.07 0.49 D a

Chlorobenzene 112.56 0.25 C a

Chlorodifluoromethane 86.47 1.30 C

Chloroethane (ethyl chloride) 64.52 1.25 B a

Chloroform 119.39 0.03 B a

Chloromethane 50.49 1.21 B

Dichlorobenzene 147 0.21 E c

Dichlorodifluoromethane 120.91 15.7 A

Dichlorofluoromethane 102.92 2.62 D

Dichloromethane (methylene chloride) 84.94 14.3 A a

Dimethyl sulfide (methyl sulfide) 62.13 7.82 C

Ethane 30.07 889 C

Ethanol 46.08 27.2 E

Ethyl mercaptan (ethanethiol) 62.13 2.28 D

Ethylbenzene 106.16 4.61 B a

Ethylene dibromide 187.88 0.001 E

Fluorotrichloromethane 137.38 0.76 B

Hexane 86.18 6.57 B a

Hydrogen sulfide 34.08 35.5 B

Mercury (total) 200.61 2.92x10 E a,d -4
Table 2.4-1. (Concluded)

Compound Molecular Weight (ppmv) Rating

Default

Concentration Emission Factor

11/98 Solid Waste Disposal 2.4-11

Methyl ethyl ketone 72.11 7.09 A a

Methyl isobutyl ketone 100.16 1.87 B a

Methyl mercaptan 48.11 2.49 C

Pentane 72.15 3.29 C

Perchloroethylene (tetrachloroethylene) 165.83 3.73 B a

Propane 44.09 11.1 B

t-1,2-dichloroethene 96.94 2.84 B

Trichloroethylene (trichloroethene) 131.40 2.82 B a

Vinyl chloride 62.50 7.34 B a

Xylenes 106.16 12.1 B a

NOTE: This is not an all-inclusive list of potential LFG constituents, only those for which test data were

available at multiple sites. References 10-67. Source Classification Codes in parentheses.

 Hazardous Air Pollutants listed in Title III of the 1990 Clean Air Act Amendments. a

 Carbon monoxide is not a typical constituent of LFG, but does exist in instances involving landfill b

(underground) combustion. Therefore, this default value should be used with caution. Of 18 sites where CO was

measured, only 2 showed detectable levels of CO.

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

III-listed HAP.

 No data were available to speciate total Hg into the elemental and organic forms. d
2.4-12 EMISSION FACTORS 11/98

Table 2.4-2. DEFAULT CONCENTRATIONS OF BENZENE, NMOC, AND TOLUENE BASED ON WASTE

DISPOSAL HISTORYa

(SCC 50100402, 50300603)

Pollutant Weight (ppmv) Rating

Molecular Concentration Emission Factor

Default

Benzene 78.11 b

 Co-disposal 11.1 D

 No or Unknown co-disposal 1.91 B

NMOC (as hexane) 86.18 c

 Co-disposal 2420 D

 No or Unknown co-disposal 595 B

Toluene 92.13 b

 Co-disposal 165 D

 No or Unknown co-disposal 39.3 A

 References 10-54. Source Classification Codes in parentheses. a

 Hazardous Air Pollutants listed in Title III of the 1990 Clean Air Act Amendments. b

 For NSPS/Emission Guideline compliance purposes, the default concentration for NMOC as c

specified in the final rule must be used. For purposes not associated with NSPS/Emission

Guideline compliance, the default VOC content at co-disposal sites = 85 percent by weight

(2,060 ppmv as hexane); at No or Unknown sites = 39 percent by weight 235 ppmv as hexane). 
11/98 Solid Waste Disposal 2.4-13

Table 2.4-3. CONTROL EFFICIENCIES FOR LFG CONSTITUENTSa

Control Device Constituent Typical Range Rating b

Control Efficiency (%)

Boiler/Steam Turbine NMOC 98.0 96-99+ D

(50100423)

Flarec

(50100410)

(50300601)

Halogenated Species 99.6 87-99+ D

Non-Halogenated Species 99.8 67-99+ D

NMOC 99.2 90-99+ B

Halogenated Species 98.0 91-99+ C

Non-Halogenated Species 99.7 38-99+ C

Gas Turbine NMOC 94.4 90-99+ E

(50100420)

IC Engine NMOC 97.2 94-99+ E

(50100421)

Halogenated Species 99.7 98-99+ E

Non-Halogenated Species 98.2 97-99+ E

Halogenated Species 93.0 90-99+ E

Non-Halogenated Species 86.1 25-99+ E

 References 10-67. Source Classification Codes in parentheses. a 

 Halogenated species are those containing atoms of chlorine, bromine, fluorine, or iodine. For any b

equipment, the control efficiency for mercury should be assumed to be 0. See section 2.4.4.2 for

methods to estimate emissions of SO , CO , and HCl. 2 2

 Where information on equipment was given in the reference, test data were taken from enclosed flares. c

Control efficiencies are assumed to be equally representative of open flares.
2.4-14 EMISSION FACTORS 11/98

Table 2.4-4. (Metric Units) EMISSION FACTORS FOR SECONDARY COMPOUNDS

EXITING CONTROL DEVICESa

Control Device Pollutant Methane Rating b kg/10 dscm Emission Factor 6

Flarec

(50100410)

(50300601)

Nitrogen dioxide 650 C

Carbon monoxide 12,000 C

Particulate matter 270 D

IC Engine Nitrogen dioxide 4,000 D

(50100421) Carbon monoxide 7,500 C

Particulate matter 770 E

Boiler/Steam Turbine Nitrogen dioxide 530 D d

(50100423) Carbon monoxide 90 E

Particulate matter 130 D

Gas Turbine Nitrogen dioxide 1,400 D

(50100420) Carbon monoxide 3,600 E

Particulate matter 350 E

 Source Classification Codes in parentheses. Divide kg/10 dscm by 16,700 to obtain kg/hr/dscmm. a 6

 No data on PM size distributions were available, however for other gas-fired combustion sources, most b

of the particulate matter is less than 2.5 microns in diameter. Hence, this emission factor can be used to

provide estimates of PM-10 or PM-2.5 emissions. See section 2.4.4.2 for methods to estimate CO , 2

SO , and HCl. 2

 Where information on equipment was given in the reference, test data were taken from enclosed flares. c

Control efficiencies are assumed to be equally representative of open flares.

 All source tests were conducted on boilers, however emission factors should also be representative of d

steam turbines. Emission factors are representative of boilers equipped with low-NO burners and flue x

gas recirculation. No data were available for uncontrolled NO emissions. x
11/98 Solid Waste Disposal 2.4-15

Table 2.4-5. (English Units) EMISSION RATES FOR SECONDARY COMPOUNDS

EXITING CONTROL DEVICESa

Control Device Pollutant Methane Factor Rating b

 lb/10 dscf Emission 6

Flare Nitrogen dioxide 40 C c

(50100410) Carbon monoxide 750 C

(50300601) Particulate matter 17 D

IC Engine Nitrogen dioxide 250 D

(50100421) Carbon monoxide 470 C

Particulate matter 48 E

Boiler/Steam Turbine Nitrogen dioxide 33 E d

(50100423) Carbon monoxide 5.7 E

Particulate matter 8.2 E

Gas Turbine Nitrogen dioxide 87 D

(50100420) Carbon monoxide 230 D

Particulate matter 22 E

 Source Classification Codes in parentheses. Divide lb/10 dscf by 16,700 to obtain lb/hr/dscfm. a 6

 Based on data for other combustion sources, most of the particulate matter will be less than 2.5 b

microns in diameter. Hence, this emission rate can be used to provide estimates of PM-10 or

PM-2.5 emissions. See section 2.4.4.2 for methods to estimate CO , SO , and HCl. 2 2

 Where information on equipment was given in the reference, test data were taken from enclosed c

flares. Control efficiencies are assumed to be equally representative of open flares.

 All source tests were conducted on boilers, however emission factors should also be d

representative of steam turbines. Emission factors are representative of boilers equipped with

low-NO burners and flue gas recirculation. No data were available for uncontrolled NO x x

emissions.

References for Section 2.4

1. "Criteria for Municipal Solid Waste Landfills," 40 CFR Part 258, Volume 56, No. 196, October 9,

1991.

2. Air Emissions from Municipal Solid Waste Landfills - Background Information for Proposed

Standards and Guidelines, Office of Air Quality Planning and Standards, EPA-450/3-90-011a,

Chapters 3 and 4, U. S. Environmental Protection Agency, Research Triangle Park, NC, March 1991.

3. Characterization of Municipal Solid Waste in the United States: 1992 Update, Office of Solid Waste,

EPA-530-R-92-019, U. S. Environmental Protection Agency, Washington, DC, NTIS

No. PB92-207-166, July 1992.

4. Eastern Research Group, Inc., List of Municipal Solid Waste Landfills, Prepared for the

U. S. Environmental Protection Agency, Office of Solid Waste, Municipal and Industrial Solid Waste

Division, Washington, DC, September 1992.

5. Suggested Control Measures for Landfill Gas Emissions, State of California Air Resources Board,

Stationary Source Division, Sacramento, CA, August 1990.
2.4-16 EMISSION FACTORS 11/98

6. "Standards of Performance for New Stationary Sources and Guidelines for Control of Existing Sources: 

Municipal Solid Waste Landfills; Proposed Rule, Guideline, and Notice of Public Hearing," 40 CFR

Parts 51, 52, and 60, Vol. 56, No. 104, May 30, 1991.

7. S.W. Zison, Landfill Gas Production Curves: Myth Versus Reality, Pacific Energy, City of Commerce,

CA, [Unpublished]

8. R.L. Peer, et al., Memorandum Methodology Used to Revise the Model Inputs in the Municipal Solid

Waste Landfills Input Data Bases (Revised), to the Municipal Solid Waste Landfills Docket No. A-88-

09, April 28, 1993. 

9. A.R. Chowdhury, Emissions from a Landfill Gas-Fired Turbine/Generator Set, Source Test Report

C-84-33, Los Angeles County Sanitation District, South Coast Air Quality Management District, June

28, 1984.

10. Engineering-Science, Inc., Report of Stack Testing at County Sanitation District Los Angeles Puente

Hills Landfill, Los Angeles County Sanitation District, August 15, 1984.

11. J.R. Manker, Vinyl Chloride (and Other Organic Compounds) Content of Landfill Gas Vented to an

Inoperative Flare, Source Test Report 84-496, David Price Company, South Coast Air Quality

Management District, November 30, 1984.

12. S. Mainoff, Landfill Gas Composition, Source Test Report 85-102, Bradley Pit Landfill, South Coast

Air Quality Management District, May 22, 1985.

13. J. Littman, Vinyl Chloride and Other Selected Compounds Present in A Landfill Gas Collection

System Prior to and after Flaring, Source Test Report 85-369, Los Angeles County Sanitation District,

South Coast Air Quality Management District, October 9, 1985.

14. W.A. Nakagawa, Emissions from a Landfill Exhausting Through a Flare System, Source Test Report

85-461, Operating Industries, South Coast Air Quality Management District, October 14, 1985.

15. S. Marinoff, Emissions from a Landfill Gas Collection System, Source Test Report 85-511. Sheldon

Street Landfill, South Coast Air Quality Management District, December 9, 1985.

16. W.A. Nakagawa, Vinyl Chloride and Other Selected Compounds Present in a Landfill Gas Collection

System Prior to and after Flaring, Source Test Report 85-592, Mission Canyon Landfill, Los Angeles

County Sanitation District, South Coast Air Quality Management District, January 16, 1986.

17. California Air Resources Board, Evaluation Test on a Landfill Gas-Fired Flare at the BKK Landfill

Facility, West Covina, CA, ARB-SS-87-09, July 1986.

18. S. Marinoff, Gaseous Composition from a Landfill Gas Collection System and Flare, Source Test

Report 86-0342, Syufy Enterprises, South Coast Air Quality Management District, August 21, 1986.

19. Analytical Laboratory Report for Source Test, Azusa Land Reclamation, June 30, 1983, South Coast

Air Quality Management District.

20. J.R. Manker, Source Test Report C-84-202, Bradley Pit Landfill, South Coast Air Quality Management

District, May 25, 1984.

21. S. Marinoff, Source Test Report 84-315, Puente Hills Landfill, South Coast Air Quality Management

District, February 6, 1985.

22. P.P. Chavez, Source Test Report 84-596, Bradley Pit Landfill, South Coast Air Quality Management

District, March 11, 1985.
11/98 Solid Waste Disposal 2.4-17

23. S. Marinoff, Source Test Report 84-373, Los Angeles By-Products, South Coast air Quality

Management District, March 27, 1985.

24. J. Littman, Source Test Report 85-403, Palos Verdes Landfill, South Coast Air Quality Management

District, September 25, 1985.

25. S. Marinoff, Source Test Report 86-0234, Pacific Lighting Energy Systems, South Coast Air Quality

Management District, July 16, 1986.

26. South Coast Air Quality Management District, Evaluation Test on a Landfill Gas-Fired Flare at the

Los Angeles County Sanitation District's Puente Hills Landfill Facility, [ARB/SS-87-06],

Sacramento, CA, July 1986.

27. D.L. Campbell, et al., Analysis of Factors Affecting Methane Gas Recovery from Six Landfills, Air

and Energy Engineering Research Laboratory, EPA-600/2-91-055, U. S. Environmental Protection

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28. Browning-Ferris Industries, Source Test Report, Lyon Development Landfill, August 21, 1990.

29. X.V. Via, Source Test Report, Browning-Ferris Industries, Azusa Landfill.

30. M. Nourot, Gaseous Composition from a Landfill Gas Collection System and Flare Outlet. Laidlaw

Gas Recovery Systems, to J.R. Farmer, OAQPS:ESD, December 8, 1987.

31. D.A. Stringham and W.H. Wolfe, Waste Management of North America, Inc., to J.R. Farmer,

OAQPS:ESD, January 29, 1988, Response to Section 114 questionnaire.

32. V. Espinosa, Source Test Report 87-0318, Los Angeles County Sanitation District Calabasas Landfill,

South Coast Air Quality Management District, December 16, 1987.

33. C.S. Bhatt, Source Test Report 87-0329, Los Angeles County Sanitation District, Scholl Canyon

Landfill, South Coast Air Quality Management District, December 4, 1987.

34. V. Espinosa, Source Test Report 87-0391, Puente Hills Landfill, South Coast Air Quality Management

District, February 5, 1988.

35. V. Espinosa, Source Test Report 87-0376, Palos Verdes Landfill, South Coast Air Quality Management

District, February 9, 1987.

36. Bay Area Air Quality Management District, Landfill Gas Characterization, Oakland, CA, 1988. 

37. Steiner Environmental, Inc., Emission Testing at BFI's Arbor Hills Landfill, Northville, Michigan,

September 22 through 25, 1992, Bakersfield, CA, December 1992.

38. PEI Associates, Inc., Emission Test Report - Performance Evaluation Landfill-Gas Enclosed Flare,

Browning Ferris Industries, Chicopee, MA, 1990.

39. Kleinfelder Inc., Source Test Report Boiler and Flare Systems, Prepared for Laidlaw Gas Recovery

Systems, Coyote Canyon Landfill, Diamond Bar, CA, 1991.

40. Bay Area Air Quality Management District, McGill Flare Destruction Efficiency Test Report for

Landfill Gas at the Durham Road Landfill, Oakland, CA, 1988. 

41. San Diego Air Pollution Control District, Solid Waste Assessment for Otay Valley/Annex Landfill. San

Diego, CA, December 1988.
2.4-18 EMISSION FACTORS 11/98

42. PEI Associates, Inc., Emission Test Report - Performance Evaluation Landfill Gas Enclosed Flare,

Rockingham, VT, September 1990.

43. Browning-Ferris Industries, Gas Flare Emissions Source Test for Sunshine Canyon Landfill. Sylmar,

CA, 1991.

44. Scott Environmental Technology, Methane and Nonmethane Organic Destruction Efficiency Tests of

an Enclosed Landfill Gas Flare, April 1992.

45. BCM Engineers, Planners, Scientists and Laboratory Services, Air Pollution Emission Evaluation

Report for Ground Flare at Browning Ferris Industries Greentree Landfill, Kersey, Pennsylvania. 

Pittsburgh, PA, May 1992.

46. EnvironMETeo Services Inc., Stack Emissions Test Report for Ameron Kapaa Quarry, Waipahu, HI,

January 1994.

47. Waukesha Pearce Industries, Inc., Report of Emission Levels and Fuel Economies for Eight Waukesha

12V-AT25GL Units Located at the Johnston, Rhode Island Central Landfill, Houston TX, July 19,

1991.

48. Mostardi-Platt Associates, Inc., Gaseous Emission Study Performed for Waste Management of North

America, Inc., CID Environmental Complex Gas Recovery Facility, August 8, 1989. Chicago, IL,

August 1989.

49. Mostardi-Platt Associates, Inc., Gaseous Emission Study Performed for Waste Management of North

America, Inc., at the CID Environmental Complex Gas Recovery Facility, July 12-14, 1989. Chicago,

IL, July 1989.

50. Browning-Ferris Gas Services, Inc., Final Report for Emissions Compliance Testing of One Waukesha

Engine Generator, Chicopee, MA, February 1994.

51. Browning-Ferris Gas Services, Inc., Final Report for Emissions Compliance Testing of Three

Waukesha Engine Generators, Richmond, VA, February 1994.

52. South Coast Environmental Company (SCEC), Emission Factors for Landfill Gas Flares at the

Arizona Street Landfill, Prepared for the San Diego Air Pollution Control District, San Diego, CA,

November 1992.

53. Carnot, Emission Tests on the Puente Hills Energy from Landfill Gas (PERG) Facility - Unit 400,

September 1993, Prepared for County Sanitation Districts of Los Angeles County, Tustin, CA,

November 1993. 

54. Pape & Steiner Environmental Services, Compliance Testing for Spadra Landfill Gas-to-Energy

Plant, July 25 and 26, 1990, Bakersfield, CA, November 1990.

55. AB2588 Source Test Report for Oxnard Landfill, July 23-27, 1990, by Petro Chem Environmental

Services, Inc., for Pacific Energy Systems, Commerce, CA, October 1990. 

56. AB2588 Source Test Report for Oxnard Landfill, October 16, 1990, by Petro Chem Environmental

Services, Inc., for Pacific Energy Systems, Commerce, CA, November 1990. 

57. Engineering Source Test Report for Oxnard Landfill, December 20, 1990, by Petro Chem

Environmental Services, Inc., for Pacific Energy Systems, Commerce, CA, January 1991. 

58. AB2588 Emissions Inventory Report for the Salinas Crazy Horse Canyon Landfill, Pacific Energy,

Commerce, CA, October 1990.
11/98 Solid Waste Disposal 2.4-19

59. Newby Island Plant 2 Site IC Engine's Emission Test, February 7-8, 1990, Laidlaw Gas Recovery

Systems, Newark, CA, February 1990.

60. Landfill Methane Recovery Part II: Gas Characterization, Final Report, Gas Research Institute,

December 1982.

61. Letter from J.D. Thornton, Minnesota Pollution Control Agency, to R. Myers, U.S. EPA, February 1,

1996.

62. Letter and attached documents from M. Sauers, GSF Energy, to S. Thorneloe, U.S. EPA, May 29, 1996.

63. Landfill Gas Particulate and Metals Concentration and Flow Rate, Mountaingate Landfill Gas Recovery

Plant, Horizon Air Measurement Services, prepared for GSF Energy, Inc., May 1992.

64. Landfill Gas Engine Exhaust Emissions Test Report in Support of Modification to Existing IC Engine

Permit at Bakersfield Landfill Unit #1, Pacific Energy Services, December 4, 1990.

65. Addendum to Source Test Report for Superior Engine #1 at Otay Landfill, Pacific Energy Services,

April 2, 1991.

66. Source Test Report 88-0075 of Emissions from an Internal Combustion Engine Fueled by Landfill Gas,

Penrose Landfill, Pacific Energy Lighting Systems, South Coast Air Quality Management District,

February 24, 1988.

67. Source Test Report 88-0096 of Emissions from an Internal Combustion Engine Fueled by Landfill Gas,

Toyon Canyon Landfill, Pacific Energy Lighting Systems, March 8, 1988.

68. Letter and attached documents from C. Nesbitt, Los Angeles County Sanitation Districts, to K. Brust,

E.H. Pechan and Associates, Inc., December 6, 1996.

69. Determination of Landfill Gas Composition and Pollutant Emission Rates at Fresh Kills Landfill,

revised Final Report, Radian Corporation, prepared for U.S. EPA, November 10, 1995.

70. Advanced Technology Systems, Inc., Report on Determination of Enclosed Landfill Gas Flare

Performance, Prepared for Y & S Maintenance, Inc., February 1995. 

71. Chester Environmental, Report on Ground Flare Emissions Test Results, Prepared for Seneca Landfill,

Inc., October 1993.

72. Smith Environmental Technologies Corporation, Compliance Emission Determination of the Enclosed

Landfill Gas Flare and Leachate Treatment Process Vents, Prepared for Clinton County Solid Waste

Authority, April 1996. 

73. AirRecon®, Division of RECON Environmental Corp., Compliance Stack Test Report for the Landfill

Gas FLare Inlet & Outlet at Bethlehem Landfill, Prepared for LFG Specialties Inc., December 3, 1996. 

74. ROJAC Environmental Services, Inc., Compliance Test Report, Hartford Landfill Flare Emissions

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75. Normandeau Associates, Inc., Emissions Testing of a Landfill Gas Flare at Contra Costa Landfill,

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76. Roe, S.M., et. al., Methodologies for Quantifying Pollution Prevention Benefits from Landfill Gas

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