SWICS Methane Oxidization Addendum 2012

1

SWICS 2.2 Methane Oxidation Addendum 2012

November 19, 2012

ABSTRACT

In July 2007, the Solid Waste Industry for Climate Solutions (SWICS) released its first white 

paper titled Current MSW Industry Position and State-of-the-Practice on LFG Collection 

Efficiency, Methane Oxidation, and Carbon Sequestration in Landfills (White Paper). In January 

2009, SWICS updated the White Paper to incorporate additional studies and update the 

approach. At that time 47 published evaluations were available. This current addendum to the 

2009 White Paper includes methane oxidation results from evaluations of cover soils at 90 

landfills. The revised values are shown below.

Table 1 – Methane Oxidation Summary

Cover Type Mean Percent Oxidized

(standard error*)

Median

Percent

Oxidized

Number of Landfills 

Included in Evaluation

Organic Covers 38 (7) 37 12

Clay Cover 30 (3) 29 32

Sand Cover 54 (5) 50 16

Other Mixtures 36 (5) 30 30

Overall 38 (3) 33 90

*Standard error is the standard deviation of the mean divided by the square root of “n”, where “n” is the number of 

values in Table 2. 

This addendum also addresses the primary concerns raised following release of the SWICS 2009 

White Paper. 

• First, some questioned the decision to calculate oxidation values using the arithmetic 

means of the data, as opposed to the median value, because it appeared that the means 

might be biased high. A more thorough discussion of this issue, including more recent 

literature, is included in the addendum, and both median and mean values are provided.

• Second, some concern was expressed regarding possible over-reliance on laboratory 

studies, which tend to yield higher oxidation fractions. Since release of the 2009 White 

Paper, a significant number of additional field measurements have been made, and these 

results are included in the addendum.

• Third, only five field measurements for clay soils were available during development of 

the 2009 White Paper. Since then, significant effort was made to incorporate the results 

of 31 field studies.

• Fourth, we have addressed the variation in methane oxidation with the methane emission 

rate.
SWICS Methane Oxidization Addendum 2012

2

INTRODUCTION

The purpose of this addendum is to update the oxidation values in the 2009 White Paper with 

recent values derived from the published literature. Oxidation rates from literature published 

after the SWICS document were combined with those listed Table 4.1 of the 2009 White Paper. 

The 2009 White Paper described the process of methane oxidation and approaches towards 

quantifying it, and this part of the document is still current. 

Since the release of the 2009 White Paper, a number of studies have been published in peerreviewed literature, most notably an entire special issue of the journal Waste Management (2011) 

on Landfill Gas Emission and Mitigation sponsored by Consortium for Landfill Emissions 

Abatement Research (CLEAR). CLEAR is an International Waste Working Group (IWWG) 

Task Group which focuses on landfill gas emission to the atmosphere. The group has members 

from 12 countries, across four continents. A number of papers in the special issue focus on the 

use of compost biocovers, bio-windows or permeable gas dispersion layers to treat and oxidize 

landfill gas in situ (Huber-Humer et al., 2011; Pedersen et al., 2011; Scheutz et al., 2011; 

Pawlowska et al., 2011; Dever et al., 2011; and Jung et al., 2011). Additionally, several papers 

in the special issue, Ranchor et al., (2011); Abichou et al., (2011) and Chanton et al., (2011b), 

examined the response of the methane oxidizing microbial community to methane loading to the 

cover soil. 

Two key papers, Bogner et al., (2011), and Spokas et al., (2011), describe recent work in 

California where field measurements of emission and oxidation were coupled with extensive 

modeling efforts. Chanton et al., (2011a) published the results of 37 seasonal sampling events at 

20 landfills with intermediate covers over a four-year period. Abichou et al. (2011b) examined 

the best approach towards describing central tendencies in oxidation data and reported that the 

results were generally distributed normally so that mean values could be used. 

The revised Table from the 2009 White Paper (Table 1) is presented below as Table 2. As 

before, studies are grouped by soil type. 
SWICS Methane Oxidization Addendum 2012

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Table 2. Summary of studies of methane oxidation to date

Material Method Rate SE1 Rate

Fraction 

Oxidized

SE 

Fraction

Gas 

Collection

Soil Temp. (C), 

or Month and 

State Reference

ORGANIC COLUMN

Compost Repacked column with CH4 

advection

9.423 nr 1.00 nr na 18 Humer and Lechner, 1999

Compost Repacked column with CH4 

advection

6.250 0.6250 0.19 0.019 na 22 Wilshusen et al., 2004

ORGANIC COLUMN MEAN MEAN

SUMMARY STATISTICS 7.836 0.60

ORGANIC FIELD

Compost landfill cover Field isotope chamber collected 0.041 0.0331 0.55 0.136 yes Apr, Jun, Sep in KY Barlaz et al., 2004

wood chips and sludge Isotopic analysis of whole 

landfill plume

nr nr 0.16 0.031 yes 7 Borjesson et al., 2007

wood chips and sludge Isotopic analysis of whole 

landfill plume

nr nr 0.25 0.003 yes 17 Borjesson et al., 2007

Compost Field isotope chamber collected nr nr 0.29 0.065 no all year, FL Chanton et al., 2008

Compost Field soil gas probe isotope 

method

nr nr 0.44 0.048 no all year, FL Chanton et al., 2008

Mulch Field isotope chamber collected nr nr 0.00 0.045 no all year, FL Chanton et al., 2008

Mulch Field soil gas probe isotope 

method

nr nr 0.37 0.031 no all year, FL Chanton et al., 2008

Mulch Field isotope chamber collected nr nr 0.40 0.033 no all year, FL Chanton et al., 2008

Mulch Field soil gas probe isotope 

method

nr nr 0.59 0.046 no all year, FL Chanton et al., 2008

Yard-waste compost Field isotope chamber collected 0.108 0.0338 0.38 0.031 no all year, FL Stern et al., 2007

ORGANIC FIELD MEAN MEAN SE MEDIAN

SUMMARY STATISTICS 0.074 0.34 0.056 0.374 

ORGANIC ALL 3.955 0.38 0.070 0.374
SWICS Methane Oxidization Addendum 2012

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Material Method Rate SE1 Rate

Fraction 

Oxidized

SE 

Fraction

Gas 

Collection

Soil Temp. (C), 

or Month and 

State Reference

CLAY COLUMN

silty clay landfill cover Undisturbed column with 135 

to 145 ppmv CH4 diffusion

0.004 0.0005 nr nr na Jun, Sep, Nov in IL Bogner et al., 1997

silty clay landfill cover Undisturbed column with 1 to 8 

% CH4 diffusion

1.156 0.2927 nr nr na Jun, Sep, Nov in IL Bogner et al., 1997

Clay landfill cover Repacked column with CH4 

advection

6.800 0.3000 0.40 0.018 na 19 Kightley et al., 1995

CLAY COLUMN MEAN MEAN SE MEDIAN

SUMMARY STATISTICS 2.653 0.40

CLAY FIELD

Sandy clay landfill cover Field isotope chamber collected 0.564 0.3420 0.14 0.039 no Feb to May in FL Abichou et al., 2006

Clay landfill cover Field isotope chamber collected 1.216 0.8693 0.21 0.056 yes Apr, Jun,Sep in KY Barlaz et al., 2004

Clay landfill cover Field isotope chamber collected 13.517 1.8114 0.14 0.020 no 6 to 32 Chanton and Liptay, 2000

Clayey landfill cover Field isotope chamber collected nr nr 0.08 0.030 no all year, FL Chanton et al., 2008

Clayey landfill cover Field soil gas probe isotope 

method

nr nr 0.34 0.054 no all year, FL Chanton et al., 2008

Clay, Al CA Field isotope surface air 0.056 0.0120 0.27 0.08 yes Oct 2009 Chanton et al., 2011

Clay, TC CA Field isotope surface air 0.505 0.1480 0.24 0.12 yes Feb 208 Chanton et al., 2011

Clay, TC CA Field isotope surface air 1.349 0.0000 0.33 0.04 yes Aug 2008 Chanton et al., 2011

Clay, RW CA Field isotope surface air 2.431 1.8200 0.51 0.23 yes June 2009 Chanton et al., 2011

Clay, OS MN Field isotope surface air 30.729 8.0800 0.33 0.07 yes August 2007 Chanton et al., 2011

Clay, NS MN Field isotope surface air 4.112 0.0000 0.95 0.03 yes Aug 2007 Chanton et al., 2011

Clay, Met WI Field isotope surface air 7.722 2.8950 0.16 0.09 yes May 2008 WI Chanton et al., 2011

Clay, SP MN Field isotope surface air 10.079 0.0000 0.47 0.03 yes July 2008 Chanton et al., 2011

Clay MeT WI Field isotope surface air 22.920 8.6000 0.31 0.12 yes Oct 2008 Chanton et al., 2011

Clay OL 7 KY Field isotope surface air 22.820 0.0000 0.20 0.04 yes July 2006 Chanton et al., 2011

Clay OL 7 KY Field isotope surface air 10.760 5.3000 0.31 0.15 yes March 2007 Chanton et al., 2011

Clay OL 5 KY Field isotope surface air 15.627 3.8900 0.41 0.16 yes July 2007 Chanton et al., 2011

Clay OL 7 KY Field isotope surface air 6.512 0.0000 0.53 0.12 yes July 2007 Chanton et al., 2011

Clay OL 5 KY Field isotope surface air 7.470 0.0000 0.43 0.06 yes August 2007 Chanton et al., 2011
SWICS Methane Oxidization Addendum 2012

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Material Method Rate SE1 Rate

Fraction 

Oxidized

SE 

Fraction

Gas 

Collection

Soil Temp. (C), 

or Month and 

State Reference

Clay OL 7 KY Field isotope surface air 0.688 0.2390 0.28 0.12 yes December 2007 Chanton et al., 2011

Clay OL 7 KY Field isotope surface air 1.982 0.0000 0.29 0.07 yes January 2008 Chanton et al., 2011

Clay MW VA Field isotope surface air 1.927 0.1500 0.31 0.16 yes April 2008 Chanton et al., 2011

Clay MW VA Field isotope surface air 16.700 0.0000 0.41 0.05 yes Sept 2008 Chanton et al., 2011

Clay SH FL Field isotope surface air 11.100 0.7220 0.29 0.16 yes May 2006 Chanton et al., 2011

Clay SH FL Field isotope surface air 6.274 1.8000 0.20 0.08 yes Aprils 207 Chanton et al., 2011

Clay At TX Field isotope surface air 16.736 7.9200 0.30 0.15 yes Feb 2008 Chanton et al., 2011

Clay At TX Field isotope surface air 15.318 4.2800 0.13 0.08 yes November 2008 Chanton et al., 2011

Clay CV MS Field isotope surface air 1.079 0.1470 0.14 0.08 yes April 2009 Chanton et al., 2011

Clay CV MS Field isotope surface air 0.365 0.1480 0.15 0.09 yes Nov 2009 Chanton et al., 2011

Clay PR MS Field isotope surface air 2.295 0.5300 0.22 0.01 yes December 2009 Chanton et al., 2011

Clay PR MS Field isotope surface air 1.223 0.3830 0.11 0.05 yes Aprils 2009 Chanton et al., 2011

CLAY FIELD MEAN MEAN SE MEDIAN

SUMMARY STATISTICS 8.072 0.30 0.031 0.288

CLAY ALL 7.564 0.30 0.030 0.289

SAND COLUMN

Coarse sand landfill cover Repacked column with CH4 

advection

10.400 0.1000 0.61 0.006 na 19 Kightley et al., 1995

Fine sand landfill cover Repacked column with CH4 

advection

6.900 0.3000 0.41 0.018 na 19 Kightley et al., 1995

loamy sand landfill cover Repacked column with CH4 

advection of 4.8 mol m-2 d-1

4.608 0.0842 0.96 0.017 na 22 Scheutz and Kjeldsen, 2003

loamy sand landfill cover Repacked column with CH4 

advection of 65 mol m-2 d-1

23.725 1.7299 0.37 0.027 na 22 Scheutz and Kjeldsen, 2003

sandy soil Repacked column with CH4 

advection

4.366 0.2634 0.44 0.033 na 30 to 40 Visvanathan et al., 1999

sandy soil Repacked column with CH4 

advection

0.77 na not reported Ahn et al., 2002&

sand fractions .25 to 4 mm 0.52 na not reported Pawlowska et al., 2003&

cited by Rachor et al 2011

SAND COLUMN MEAN MEAN SE MEDIAN

SUMMARY STATISTICS 10.000 0.58 0.081 0.520
SWICS Methane Oxidization Addendum 2012

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Material Method Rate SE1 Rate

Fraction 

Oxidized

SE 

Fraction

Gas 

Collection

Soil Temp. (C), 

or Month and 

State Reference

SAND FIELD

Sand landfill cover Field isotope chamber collected 0.172 0.2771 0.42 0.095 no 0.4 to 24.8 Borjesson et al., 2001

Sand adjacent to landfill Field CH4 and CO2 mass 

balance 

1.097 0.4969 0.89 nr nr 2 to 25 Christophersen et al., 2001

Sand adjacent to landfill Field isotope chamber collected 0.149 0.1372 0.28 0.152 nr 2 to 25 Christophersen et al., 2001

Sand KC CA Field isotope surface air 0.024 0.0100 0.56 0.24 yes Jan 208 Chanton et al., 2011

Sand KC CA Field isotope surface air 0.078 0.0000 0.69 0.07 yes June 2008 Chanton et al., 2011

Sand Marina CA Field isotope chamber collected 0.30 0.020 yes annual cycle Bogner et al. 2011

Sand Marina CA soil gas probe isotope method 0.40 0.032 yes annual cycle Bogner et al. 2011

Sand Scholl, CA Field isotope chamber collected 0.52 0.180 yes annual cycle Bogner et al. 2011

Sand Scholl, CA soil gas probe isotope method 0.48 0.016 yes annual cycle Bogner et al. 2011

SAND FIELD MEAN MEAN SE MEDIAN

SUMMARY STATISTICS 0.304 0.50 0.064 0.476

SAND ALL 5.152 0.54 0.050 0.497

OTHER COLUMN

Sandy-clay loam landfill 

cover

Enclosed sample with CH4 

diffusion

1.830 0.2642 0.10 nr no 19 Czepiel et al., 1996

Loamy agricultural soil Repacked column with CH4 

advection

8.236 0.2725 0.61 0.020 na 18 to 26 De Visscher et al., 1999

Sandy loam landfill cover Repacked column with CH4 

advection

15.000 0.2725 0.65 0.020 na 18 to 26 De Visscher et al., 1999

Sandy loam landfill cover Repacked column with CH4 

advection

3.535 0.0757 0.21 0.005 na 22 Hilger et al., 2000

Sand with clay landfill cover Undisturbed column with CH4 

diffusion

3.813 0.2914 nr nr na 25 Whalen et al., 1990

Loam Repacked column with CH4 

advection

0.81 nr na Scheutz et al., 2003

Loam Repacked column with CH4 

advection

0.42 nr na Humer and Lechner 2001

OTHER COLUMN MEAN MEAN SE MEDIAN

SUMMARY STATISTICS 6.483 0.47 0.112 0.517
SWICS Methane Oxidization Addendum 2012

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Material Method Rate SE1 Rate

Fraction 

Oxidized

SE 

Fraction

Gas 

Collection

Soil Temp. (C), 

or Month and 

State Reference

OTHER FIELD

Sandy loam landfill cover Field isotope chamber collected 0.456 0.2158 0.25 0.028 no Sept to Feb in FL Abichou et al., 2006

European landfill covers Field isotope chamber collected 4.239 1.5460 0.84 0.023 yes 5.8 to 26.9 Bergamaschi et al., 1998

Sandy loam landfill cover Field isotope chamber collected 3.795 2.6892 0.26 0.048 yes -0.3 to 26.8 Borjesson et al., 2001

sewage sludge and mineral 

soils

Isotopic analysis of whole 

landfill plume

nr nr 0.07 0.023 yes 6 Borjesson et al., 2007

sewage sludge and mineral 

soils

Isotopic analysis of whole 

landfill plume

nr nr 0.15 0.011 yes -2 Borjesson et al., 2007

mineral soil Isotopic analysis of whole 

landfill plume

nr nr 0.40 0.026 yes 9 Borjesson et al., 2007

mineral soil Isotopic analysis of whole 

landfill plume

nr nr 0.38 0.032 yes 5 Borjesson et al., 2007

Mulch and topsoil landfill 

cover

Field isotope chamber collected 1.678 0.2114 0.26 0.040 no 8 to 35 Chanton and Liptay, 2000

Loamy landfill cover Field isotope chamber collected nr nr 0.12 0.025 no all year, FL Chanton et al., 2008

Loamy landfill cover Field soil gas probe isotope 

method

nr nr 0.31 0.045 no all year, FL Chanton et al., 2008

Sandy-clay loam landfill 

cover

Field chambers and estimated 

fraction oxidized

0.906 0.2506 nr nr no Sept to Oct in NH Czepiel et al., 1996a

Sandy-clay loam landfill 

cover

Field plume tracer and 

estimated fraction oxidized

1.031 0.0586 nr nr no Sept to Oct in NH Czepiel et al., 1996a

Landfill "A" cover* Field isotope chamber collected nr nr 0.28 0.108 nr 21 to 30 Liptay et al., 1998

Landfill "B" cover* Field isotope chamber collected nr nr 0.19 0.014 nr 20 to 28 Liptay et al., 1998

Sandy-clay loam landfill 

cover

Field isotope chamber collected nr nr 0.68 0.093 nr 22 to 29 Liptay et al., 1998

Rochester landfill cover* Field isotope chamber collected nr nr 0.00 0.035 nr Aug in NH Liptay et al., 1998

Springfield landfill cover* Field isotope chamber collected nr nr 0.01 0.042 nr 14 to 18 Liptay et al., 1998

Wayland landfill cover* Field isotope chamber collected nr nr 0.32 0.053 nr 18 to 23 Liptay et al., 1998

Fine sandy loam landfill 

cover

Field isotope chamber collected 0.141 0.0281 0.19 0.027 no all year, FL Stern et al., 2007

Sandy clay DADS CO Field isotope surface air 0.204 0.1370 0.64 0.12 yes Oct 2007 Chanton et al., 2011

Silty clay loam SB OH Field isotope surface air 11.050 0.0000 0.25 0.04 yes Sept 2009 Chanton et al., 2011

Silty clay loam SB OH Field isotope surface air 0.712 0.2690 0.06 0.02 Dec 2009 Chanton et al., 2011

Silty clay loam + composted 

yard waste OL8 KY

Field isotope surface air 29.750 0.0000 0.70 0.04 yes July 2006 Chanton et al., 2011
SWICS Methane Oxidization Addendum 2012

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Material Method Rate SE1 Rate

Fraction 

Oxidized

SE 

Fraction

Gas 

Collection

Soil Temp. (C), 

or Month and 

State Reference

Silty clay Loam + 

composted yard waste OL8 

KY

Field isotope surface air 3.540 1.2200 0.59 0.23 yes July 2007 Chanton et al., 2011

Silty Clay Loam Cen IA Field isotope surface air 12.340 0.0000 0.82 0.06 yes August 2007 Chanton et al., 2011

Sandy Loam Atl VA Field isotope surface air 8.329 0.0000 0.34 0.04 yes Aug 2008 Chanton et al., 2011

* soil type not reported

STATISTICS MEAN MEAN SE MEDIAN

OTHER FIELD 5.584 0.34 0.051 0.272

OTHER ALL 5.820 0.36 0.047 0.297

ALL RESULTS COMBINED all cover 

types

6.456 0.38 0.02 0.33

1 “SE” refers to standard error and is defined as standard deviation/ square root (n), where n is the number of values. 
SWICS Methane Oxidization Addendum 2012

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CHANGES RELATIVE TO SWICS (2009)

Table 2 summarizes the means, medians and number of studies reported in Table 4.1 of 2009 

White Paper and the same statistics for this addendum. The sample size of published 

determinations of landfill cover oxidation has nearly doubled, from 47 observations to 90. Areas 

where there were few observations previously, for example clay covers, have been expanded. 

For other types of covers, such as organic covers which are not widely applied in the industry, a 

large number of new studies were not available. 

As shown in Table 2 of this document, the mean fraction oxidized for clay cover field studies has 

increased from a fraction oxidized of 0.18 to 0.30 while the median has increased from 0.14 to 

0.29 as the sample size has increased from 5 to 31. The number of observations in sandy soils 

has doubled with the mean value going from 0.55 to 0.54 while the median value increased from 

0.43 to 0.50 fraction oxidized. “Other” covers increased by 9 observations and both the mean 

and the median fraction oxidized values increased a bit. The overall mean of the entire study 

increased from 0.35 to 0.38 fraction oxidized while the overall median increased from 0.31 to 

0.33. 

As in the 2009 White Paper, laboratory column studies and field methods have been included in 

the average because each type of study has strengths and weaknesses as described in the 2009 

White Paper. The column results were determined by mass balance, which produces a more 

exact estimate, while the field studies often relied on isotope measurements, which yields a lower 

limit value for methane oxidation. That is, because of the nature of the measurement, the 

oxidation determinations by the isotope approach systematically underestimate oxidation 

(Chanton et al, 2011a, b). 

To explain why these isotope results are lower limits of methane oxidation, consider the 

following example (Figure 1). This figure depicts methane loading to the oxic zone of the landfill 

cover (yellow region), from the anoxic waste below (orange layer). Within the anoxic layer 

(orange) the methane is produced with a δ13C value of -60‰. This negative value indicates 13C 

depletion. Within the (yellow) oxic zone of the soil, methane is consumed by methanotrophic 

bacteria, with the result that the methane flux is attenuated (smaller arrow) while its δ13C value 

becomes more positive, as expected. The isotope approach determines methane oxidation (arrow 

size reduction) by the shift in the methane δ13C between the anoxic zone and the emitted value 

(in red in the figure). To the extent that sample collection mixes methane from emissions that 

are more and less oxidized, the sample will always be weighted (in a weighted average) towards 

the less oxidized (larger) sample. Because of this, isotope determined oxidation always is 

weighted towards the less attenuated sample, which means that the oxidation value always 

underestimates oxidation. 
SWICS Methane Oxidization Addendum 2012

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Figure 1. Depiction of methane emission and oxidation in a landfill cover soil.*

*The orange area represents the anoxic zone where methane is produced with a 

δ13C value of -60‰. The yellow area represents the oxic zone of the soil where 

methanotrophs function, consuming methane and shifting its δ13C value in the 

process. The arrows represent plumes of methane across the landfill surface 

going up to bottom of the oxic zone and emitted from the oxic zone surface. 

The shift in the δ13C of methane within and across the oxic zone is proportional 

to the amount of methane oxidized, so the arrows get smaller and increasingly 

enriched in δ13C, more positive, going to the right in the figure. If, in a sample 

collection at the surface, two such arrows or plumes are mixed, the sample will

be mass weighted towards the arrow that is larger and that has experienced less 

oxidation, so the value for oxidation that is calculated for this sample will thus 

underestimate the true value. This is because the more oxidized an arrow or 

plume is smaller in mass than the less oxidized plume and so it contributes less 

methane to the weighted average signal of the combined two plumes. 

For example in the figure above, consider the plumes marked 2 and 5. If these 

plumes are co-mingled, the % oxidation for the co-mingled sample would be 

(25% + 99%)/2 = 62%. However the isotopic value of this co-mingled plume 

would be (calculated by weighted average mass balance) 

(0.75* -53‰ ) + (0.01 * -31‰) = x (0.76); where x = -52.7‰. 

In this instance, solving for the % oxidation of a co-mingled plume with a δ13C 

value of -52.7‰ yields 29% oxidation, not 62%. The consumed plume does 

not contribute much mass to the co-mingled plume, so the isotopes are shifted 

towards the lesser oxidized methane. In this way, the isotopic technique 

always produces a lower limit estimate.

0%

-60‰

13C tracing of Methane Oxidation

25%

-53‰ 50%

-45‰ 75%

-37‰ 99%

-31‰

100%

No signal

OXIC Zone

Anoxic Zone

δ13C of CH4 = - 60‰

Bottom Flux

% oxidation

Isotope signal

Methane 

loading

2 5
SWICS Methane Oxidization Addendum 2012

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Chanton et al., (2009) reexamined the 2009 White Paper compilation and reported that fifteen of 

the studies in the 2009 White Paper report were conducted over the entire annual cycle. The

fraction of methane oxidized in these studies ranged from 11 to 89 percent and had a mean value 

of 35 ± 6 percent, a value nearly identical to the overall simple mean (Chanton et al., 2009). 

Nine of the seasonal studies were conducted in north Florida at 30o North latitude and had a 

fraction oxidized of 27 ± 4 percent. Five of the seasonal studies were conducted across northern 

Europe (approximately 50 to 55o North latitude) and exhibited an average of 54 ± 14 percent. 

The fifteen seasonal studies include the New Hampshire USA study which had a value of 10 

percent (Czepiel et al 1996). The observations added to this 2012 addendum were conducted 

throughout the year and some over annual cycles. 

The rather unexpected inverse relationship of fraction oxidized with latitude (higher oxidation at 

higher latitude) mentioned above may be influenced by two studies, Christophersen et al (2001) 

and Bergamaschi et al., (1998), which used somewhat different approaches. The carbon dioxide 

to methane (CO2/CH4) ratio approach employed by Christophersen et al., (2001) yielded 89 

percent oxidation versus 28 percent oxidation by the stable isotope technique in the same cover. 

This ratio approach has received additional interest of late (Gebert et al., 2011a). Bergamaschi et 

al., (1998) used a combined radon-stable isotope technique and determined 89 percent oxidation 

in a landfill cover. As stated above, the isotope method described by Liptay et al., (1998) and 

Chanton and Liptay (2000) yields conservative lower limit estimates. 

No trend in the data with oxidation as a function of cover thickness was observed in the studies 

compiled (Chanton et al., 2009). There may be several reasons why there is no observable trend 

with cover thickness. Oxidation is restricted to the zone within a cover where oxygen can 

penetrate via diffusion from above. Since the oxygen comes in from above, the cover thickness 

overall does not affect oxygen penetration except that a thicker cover may attenuate the upward 

advection of methane that tends to push oxygen out of the soil. Secondly, the data were 

compiled from a number of soil covers and include a variety of factors so any trend might have 

been obscured by other sources of variability. Additional controlled studies of methane 

oxidation as a function of cover thickness at a single site would need to be conducted (e.g. Stern 

et al., 2007). In general, a thicker cover will result in increased retention times for transported 

methane. This increased retention of CH4 in a landfill soil cover results in lower emission rates 

and in a higher fraction of methane being oxidized (Stern et al., 2007).
SWICS Methane Oxidization Addendum 2012

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Table 3 - Summary of Differences in Percent Oxidation between

2009 White Paper and the 2012 Addendum.

Soil Type 2009 2012

Mean SE Median Number 

of 

Studies

Mean se Median Number 

of 

Studies

Organic 

column

0.6 0.40 0.60 2 0.6 0.40 0.60 2

Organic 

field

0.34 0.06 0.38 10 0.34 0.06 0.37 10

Organic 

All

0.38 0.07 0.35 12 0.38 0.07 0.37 12

Clay 

column

0.40 0.4 1 0.40 0.4 1

Clay field 0.18 0.04 0.14 5 0.30 0.03 0.29 31

Clay all 0.22 0.05 0.18 6 0.30 0.03 0.29 32

Sand 

column

0.56 0.11 0.44 5 0.58 0.08 0.52 7

Sand 

Field

0.53 0.18 0.420 3 0.50 0.06 0.48 9

Sand all 0.55 0.09 0.43 8 0.54 0.05 0.50 16

Other 

Column

0.39 0.14 0.41 4 0.47 0.11 0.52 6

Other 

Field

0.27 0.05 0.26 17 0.34 0.05 0.27 24

Other all 0.30 0.05 0.260 21 0.36 0.05 0.30 30

Overall 0.35 0.04 0.31 47 0.38 0.03 0.33 90

SE – Standard Error

These data indicate that if a single value is considered for methane oxidation it should be on the 

order of 38 percent, significantly more than the value of 10 percent currently used by USEPA for 

regulatory, policy and inventory purposes. Alternatively, the data would support cover material 

specific values of 30 percent for clay soils, 30 percent for organic covers, 52 percent for sand 

covers, and 36 percent for other soils or mixtures. Note that Abichou et al, (2011) reported that 

methane oxidation values are normally distributed so mean values are an acceptable way to 

express the central tendencies of these data. Also note that the 2012 values for field studies only 

(excluding lab studies) yield a mean value of 34 ± 3%, with a median value of 30%. There are 

74 studies in this field only compilation.
SWICS Methane Oxidization Addendum 2012

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SOURCE OF THE CURRENT DEFAULT VALUE OF 1 0 PERCENT

The current default value for landfill methane oxidation is between 0 and 10 percent of emitted 

methane (IPCC, 2006, USEPA, 2004). The 10 percent value was first proposed at an 

Intergovernmental Panel on Climate Change (IPCC) workshop in Washington, DC in 1995. At 

an internationally attended meeting in Chicago in 1997, it was agreed to use 10 percent as a 

standard value (IPCC, 2000). The results of the comprehensive studies, which had been 

conducted in New Hampshire were just becoming widely disseminated. The earliest government 

document referring to 10 percent value for landfill methane oxidation is USEPA (1998) in which 

the USEPA cites the New Hampshire studies of Liptay et al., (1998) and Czepiel et al., (1996a, 

1996b), who published seasonally averaged annual values of 10 percent methane oxidation. Air 

plume studies later confirmed the 10 percent value (Chanton et al., 1999). The USEPA in 2004 

stated that “average oxidation of methane in some laboratory and case studies on landfill covers 

have indicated ranges from 10 percent to over 25 percent with the lower portion of the range 

being found in clay soils and higher in topsoils” (USEPA, 2004). Due to the uncertainty 

involved and the lack of a standard method for the determination of oxidation rate, the USEPA 

recommended the default factor of 10 percent methane oxidation for landfill cover soils. 

It is critical to note that the Czepiel studies (Czepiel et al., 1996a, b) were conducted at a landfill 

with no gas collection which was rather poorly maintained. According to Czepiel et al., (1996b), 

“no landfill gas control systems were in place at the time of sampling”. The site was 

characterized by “sparse or dead surface vegetation (which) was a reliable visual indicator of 

significant localized CH4 emissions.” “Erosion and slumping of the cover material along the 

south edge of the MSW landfill has exposed a section of waste approximately 2m high and 10 m 

long”. Czepiel et al. (1996b) determined surface emissions to be 16,740 liter CH4 min-1 from the

landfill. Emissions were dominated by the MSW portion of area which was of size 238,000 m2

(subtracting a tire dump). These figures result in an emission rate of 66.3 g CH4 m-2 d-1

. In the 

latter part of this document we will put these measurements into perspective. 

Interestingly, the first journal publication to report the activity of methanotrophs in landfill cover 

soils was not the Czepiel studies. Rather, Whalen et al., (1990), reported the highest rates of 

methane oxidation observed in any soils prior to that time (45 g or 3 mol m-2 day-1). Whalen et 

al., (1990) studied California landfills. Later, Kightley et al., (1995) reported that coarse sandy 

landfill soils permeated with methane for six months oxidized 10.4 mol of methane m-2 day-1. 

Whalen et al., (1990) reported that methane oxidation consumed approximately 50 percent of 

methane produced in the landfill they studied. It is unclear why Whalen’s publication did not 

receive similar attention to the work of Czepiel et al. (1996a) during the IPCC’s development of 

a default oxidation factor. Had Whalen’s publication received such attention from the agency 

during the initial rule making period, the default rate for methane oxidation might have been set 

considerably higher at the start. 

The literature summarized in this report indicates that the fraction of methane oxidized in cover 

soils is probably greater than the default value of 10 percent. Of the 90 determinations of 

methane oxidation reported in Table 1, only 4 are less than 10 percent. The Czepiel et al., 

(1996a) study reports a value of 10 percent. The default value of 10 percent should be updated 

based upon technological advancements in soil engineering and state-of-the-practice applications 

in cover design as well as recent studies detailed above. 
SWICS Methane Oxidization Addendum 2012

14

0%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90 100

Flux from Waste (g/m2/d)

oxidation (%)

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Flux from Waste (g/m2/d)

oxidation Rate (g/m2/d)

100% oxidation flux, Zero emission flux

maximum oxidation capacity

0%

20%

40%

60%

80%

100%

0 10 20 30 40 50 60 70 80 90 100

Flux from Waste (g/m2/d)

oxidation (%)

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Flux from Waste (g/m2/d)

oxidation Rate (g/m2/d)

100% oxidation flux, Zero emission flux

maximum oxidation capacity

AN ALTERNATIVE TO A SINGLE VALUE: OXIDATION AS A 

FUNCTION OF METHANE LOADING TO THE COVER

It is also important to consider how the percent methane oxidation is expressed. Currently, 

oxidation is generally expressed as a percent of the transported methane that is oxidized, i.e., a 

constant fraction of landfill methane emission (e.g., IPCC 2006, USEPA 1995, USEPA 2009). 

In this scenario, the amount of methane oxidized increases linearly as emissions increase. 

Recent studies, however, show that the percent oxidation is an inverse function of the rate of 

emission (Stern et al.,2007; Rachor et al., 2011; Chanton et al., 2011a,b). At lower emission 

rates, the methanotrophs in the soil cover can consume a larger portion of the methane delivered 

to them, potentially oxidizing 95 to 100 percent (Humer and Lechner, 1999, 2001a, HuberHumer 2008; Powelson et al., 2006, 2007; Kjeldsen et al., 1997). As out-flux rates increase, the 

percent oxidation decreases and the methanotrophs can become overwhelmed with methane. 

Thus, as methane emission increases, percent oxidation decreases (Powelson et al., 2006, 2007). 

Figure 2. From Abichou et al., (2010). Modeled relationships between methane 

oxidation rate and percent oxidation as a function of methane loading to the 

landfill cover. 
SWICS Methane Oxidization Addendum 2012

15

Figure 2, from a mathematical model of cover oxidation by (Abichou et al., 2010), demonstrates 

that at lower methane fluxes, oxidation rates are equal to the methane loading to the soil cover. 

Oxidation keeps pace with flux, and the soil cover is able to oxidize all of the methane coming 

from below. The slope of the line is equal to one (Figure 2 - top). The same data are then 

expressed as the fraction oxidized versus methane loading to the cover (Figure 2 - bottom). At 

lower loading rates, methane oxidation is equal to 100 percent. As flux increases, the cover is 

not able to oxidize all of the incoming methane, and the percent oxidation falls off. Therefore, 

percent oxidation starts to decrease as the methane loading to the cover increases. As methane 

loading to the cover increases, the oxidation rate fails to keep pace. In this model, as methane 

loading to the cover increases, the percent oxidation decreases. 

This relationship is shown clearly in the laboratory column studies of Rachor et al., (2011). At 

low methane loading rates, methane oxidation quantitatively consumes the methane input to the 

laboratory columns. As loading rates increase, the oxidation rate fails to keep pace, and the 

percent oxidation decreases. 

Figure 3. Column studies by Rachor et al., (2011)*

*Demonstrating that at low methane loading rates, methane oxidation is 

quantitative but as loading increases, the percent methane oxidation decreases. 

Differences between these columns were due to air filled porosity. 

Field studies have also confirmed this relationship between flux and percent oxidation (Chanton 

et al., 2011a,b). At low rates of methane emission, the percent oxidation is near 100 percent. 
SWICS Methane Oxidization Addendum 2012

16

As emission rates increase, the percent oxidation decreases. Note in Figure 4 that the majority of 

observations are well above the 10 percent oxidation line. 

Figure 4. Methane oxidation rate (y-axis) as a function of methane loading to 

the bottom of the landfill soil cover (x-axis) (Chanton et al.,2011b).

*The lines on the graph from left to right represent 100 percent, 50 percent, 25 

percent and 10 percent oxidation. The Czepiel et al. study is the red dot on the 

graph, and it clearly fits into the rest of the data set. The Czepiel et al study was 

conducted at a landfill with elevated methane emissions, that had no gas 

collection and that was poorly maintained as evidenced by exposed uncovered 

waste during the time of their measurements. A 10% for methane oxidation 

value at this landfill is what one would expect. 

Therefore, an alternative to using a single soil cover value for methane oxidation would be to set 

the oxidation rate as a function of methane emissions. The methane emission rate in landfill 

covers is controlled by the interrelation among the soil physical properties such as gas filled 

porosity, organic content and moisture; microbiological factors such as temperature, and 

substrate availability; and the presence or absence of a gas extraction system. Because the 

emission rate is controlled by these variables, it necessarily reflects the interplay of these 

processes. 

Figure 5 demonstrates a “bin” analysis of methane oxidation results obtained from surface landfill 

air. The emission results represent emissions through the cover soil as determined from flux 

chambers, and do not include gas leaking from pipes and vents or the working face. Over 800 

measurements are included and represent results compiled seasonally from over 20 USA landfills 

in a variety of climate types ranging from subtropical to mid-continent humid sites to 

Mediterranean and arid sites. For emissions of less than 10 grams methane m-2day-1, the best 

value for methane oxidation is 38.4 percent, for results between 10 and 70 grams methane m2

day-1 the best value is 27.4 percent, and for covers with emissions above 70 grams methane m2

day-1 the best value is 12.4 percent. 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

0 50 100 150 200

methane loading g CH4 m-2d-1 

methane oxidation g CH 4 m-2

d-1
SWICS Methane Oxidization Addendum 2012

17

Figure 5. Methane oxidation percent as a function of methane emission*

*Mean values are shown with standard error and median values below. The 

Czepiel et al (1996a,b) study had a rate of 66.3 g CH4 m-2

d-1 placing it at the high 

end of tier two. 

Table 3. Data Sort Bins <10, 10-70, >70.

Bin

bin 

lower 

limit

bin 

upper 

limit midpoint

mean 

oxidation 

rate

standard 

error

standard 

deviation N Median

<10 0.00 10.00 5.00 38.4% 1.5% 32.0% 455 33.5%

10-70 10.00 70.00 40.00 27.4% 1.7% 26.1% 225 21.0%

>70 70.00 6000.00 3035.00 12.4% 1.3% 15.3% 141 7.7%

 Bin=<10, 10-70, >70 g/m2/d

33.5%

21.0%

7.7%

n= 455, 38.4%

n= 225, 27.4%

n= 141, 12.4%

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

<10 10-70 >70

CH4 emission (g/m2/d)

CH4 oxidation (%)
SWICS Methane Oxidization Addendum 2012

18

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SWICS Methane Oxidization Addendum 2012

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Tabl e 2 F ootnotes:

Abichou et al., 2006. Oxidation rates (Jox) calculated from emission fluxes (Jout, their Table 1) and oxidation 

fractions (fox, their Table 2):

1 1 − = −

ox

out

ox f

J J (f1)

Oxidation values are from chamber collected emitted methane, mean given, error is standard error, standard 

deviation/square root of number of replicates, which were 15(sandy clay) and 31 (sandy loam).

Barlaz et al., 2004. Oxidation rates calculated using eq. f1 from Supplemental 

Information using the average emission fluxes in Tables S3 and S4 and the oxidation fractions in Table S6. 

Oxidation values are from chamber collected emitted methane, mean given, error is standard error, standard 

deviation/square root of number of replicates, which were 13 (clay) and 6 (compost).

Bergamaschi et al., 1998. The oxidation rate and SE had to be approximated by averaging the emission fluxes, 

and the SE approximated by using the average, minimum, and maximum fluxes listed for covered areas in their 

Tables 7 and 8. The oxidation rate SE accounted for propagation of error:

2

,

2

rel,a rel,b rel c s = s + s (f2)

where srel is the relative standard deviation (s mean-1

) and in this case a, b, and c refer to oxidation rate, emission 

flux rate, and fraction oxidized, respectively (Christian, 1986). The fraction oxidized SE was estimated from the 

relative SD of emitted δ13C .

Bogner et al., 1997. Oxidation estimated from their Fig. 3 for two ranges of initial CH4 concentration: 135 to 145 

ppmv and 1 to 8 percent by volume. No error estimate.

Bogner et al., 2011. chamber collected and probe collected methane, standard error is standard deviation divided 

by square root of number of replicates. N varied from 6 to 46. 

Borjesson et al., 2001. The oxidation rates and standard errors were calculated by averaging data in their Table 3 

and 5 and the propagation of error for the averages was accounted for by:

... 2

2

2

savg = s1 + s + (f3)

where savg is the standard deviation of the average and s1, s2, etc. are standard deviations of the values contributing 

to the average (Christian, 1986). 

Borjesson et al., 2007. Whole landfill analysis of upwind background and downwind plume. Error is standard 

deviation of replicate measurements divided by square root of n. 

Chanton and Liptay, 2000. The reported average oxidation rates were used with each average CH4 emission flux 

over the course of a year (estimated from their Fig. 1) to calculate oxidation rate. Error is standard error of 

monthly data averaged. Samples were collected in chambers. 

Chanton et al., 2008. Chamber collected emitted fraction oxidized from closed-system equation (their Table 1). 

SEs estimated from δ13C SEs. Subsurface samples taken from 5 to 10 cm depth with probes. 

Chanton et al. 2011. Isotope study of 20 landfills with 37 seasonal sampling events, 700 individual 

measurements. Results are based on surface air captured methane. SE in table for these data refers to half range 

between results corrected for diffusive isotopic fractionation and samples not so corrected. 

Christophersen et al., 2001. For the mass-balance method, the reported average oxidation rate for the Field 

transect, 89%, was used with each field average CH4 emission flux (their Table 1) to calculate oxidation rate. For 

the isotope fractionation method, the fraction oxidized for three locations (their Table 3) was used with the 

corresponding emission flux to calculate oxidation rate.

Czepiel et al., 1996a. Jar incubations of homogenized soil. Oxidation rate estimated from their Fig. 1 (5 - 15 cm 

depth) and assuming bulk density of 1.7 g cm3. Fraction oxidized was modeled over a year using oxidation rates 

“in soil columns” adjusted for field temperature and moisture content and field-measured outflux. This approach 

is similar to our eq. 7, 8, and 10. Standard error or other measure of confidence was not given. 

Czepiel et al., 1996b. Both chamber and plume emissions converted to oxidation rates (eq. f1) using their 

estimated oxidation fraction of 0.20. 

De Visscher et al., 1999. There are no true replicates; mean and standard error for the agricultural soil were 

estimated from repeated sampling from one column shown in their Fig. 1. Data for the landfill cover column were 

not shown; the landfill standard error was assumed to equal that for the agricultural column. 
SWICS Methane Oxidization Addendum 2012

22

Hilger et al., 2000. Oxidation values are for steady state (their Table 1, Exp. 1, Live + LFG). Oxidation rate 

calculated from column parameters. Error standard error replicate columns. 

Humer and Lechner, 1999. Oxidation values are for steady state in a single column where there was complete 

oxidation.

Liptay et al. (1998). Chamber collected emitted methane, means and standard errors given by standard deviation 

over square root n. 

Scheutz and Kjeldsen, 2003. Oxidation estimated from their Fig. 5 at inlet flow rates of 0.24 and 3.18 m3m-2d-1. 

Error estimated from replicate experiments. 

Stern et al., 2007. Chamber collected emitted methane, standard error is standard deviation over square root of n. 

N varied from 33 to 40. 

Visvanathan et al., 1999. Oxidation rates estimated from their Fig. 6.

Whalen et al., 1990. Oxidation rate is Michaelis-Menton Vmax reported on an area basis (their Table 1).

Wilshusen et al., 2004. Oxidation values are for steady state. SE was estimated from final values of three 

columns in their Fig. 2 (the low, non-steady state column was excluded). 

Ahn et al., 2002. Conference proceedings cited by Rachor et al., 2011 Compiled in their Table 5.

Pawlowska et al., 2003. Environmental Engineering Studies Kluwer Academic Publishers but reported by Rachor 

et al., 2011.

Scheutz et al., 2003. repacked column study with gas flow in from below.

Humer and Lechner, 2001. repacked column study with gas flow in from below.