### 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 Summ ary 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, som e 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

liter ature, 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

P aper, 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, significa nt 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 Pa per 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 oxid ation 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 peer

reviewed literature, most notably an entire special issue of the journ al 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 dispe rsion 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 e t 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 peri od. 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



## 3 Table 2. Summary of studies of methane oxi dati on to date

Material Method R ate SE 1 

### Rate Fraction

O xidized SE

F raction G as C ollection S oil T emp. (C),

or M onth and

S tate 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



## 4 Material Method Rate SE 1 

### 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



## 5 Material Method Rate SE 1 

### 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



## 6 Material Method Rate SE 1 

### 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



## 7 Material Method Rate SE 1 

### 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 l oam + composted

y ar d 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



## 8 Material Method Rate SE 1 

### 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 nu mber of values.

### SWICS Methane Oxidization Addendum 2012



## 9 

# 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. Th e 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 orga nic 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 0.3 0 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 mas s 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 i sotope 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 δ 13 

## C value of

- 60‰. This negative value indicates 13 

## C 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 δ 13 

## C value becomes more positive, as expected. The isotope approach determines methane oxidation (arrow size reduction) by the shift in the methane δ 13 

## C 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) t owards 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



## 10 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

δ 13 

### C value of

- 60‰. The yellow area represents the oxic zone of the soil where methanotrophs function, consuming methane and shifting its δ 13 

### C 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 δ 13 

### C of methane within and across the oxic zone i s proportional to the amount of methane oxidized, so the arrows get smaller and increasingly

enriched in δ 13 

### C, 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 smalle r 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 fo r 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, solvi ng for the % oxidation of a co

- mingled plume with a δ 13 

### C

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 wa y, the isotopic technique always produces a lower limit estimate. 

### 0%

- 60 ‰ 13 

# C tracing of Methane Oxidation

25%

- 53 ‰ 50%

- 45 ‰ 75%

- 37 ‰ 99%

- 31 ‰ 100%

No signal

OXIC Zone



### Anoxic Zone



## δ

13 

## C of CH 4 

## = - 60 ‰ Bottom Flux % oxidation Isotope signal



### Methane loading 2 5

### SWICS Methane Oxidization Addendum 2012



## 11 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 a t 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 inc lude 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 o xidized 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 (CO 2 

## /CH 4 

## ) rat io 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 ). Bergama schi 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 limi t 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 restricte d 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 methan e 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

o xidation 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 CH 4 

## 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



## 12 Table 3

- Summary of Differences in Percent Oxidation between

2009 Whit e 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 US EPA for regulatory, policy and inventory purposes. Alternatively, t he 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 value s 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%. Ther e are 74 studies in this field only compilation.

### SWICS Methane Oxidization Addendum 2012



## 13 

# SOURCE OF THE CURREN T 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 averag ed 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 indic ated 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 main tained. 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 CH 4 

## e missions.” “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 CH 4 

## min - 1 

## from the landfill. Emissions were dominated by the MSW portion of area which was of size 238,000 m 2


## (subtracting a tire dump). These figures result in an emission rate of 66.3 g CH 4 

## m - 2 

## d - 1

. 

## In the latter part of this document we will put these measurements in to perspective.

Interesting ly, 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 soi ls prior to that time (45 g or 3 mol m - 2 

## day - 1 

## ). Whalen et al., (1990) studied California landfills. L ater, 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



## . Wh alen 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 t he IPCC’s development of

a default oxidation factor

. H ad 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/m 2 

## /d)oxidation (%) 0 10 20 30 40 50 60

0 10 20 30 40 50 60 70 80 90 100


## Flux from Waste (g/m 2 

## /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/m 2 

## /d)oxidation (%) 0 10 20 30 40 50 60

0 10 20 30 40 50 60 70 80 90 100


## Flux from Waste (g/m 2 

## /d)oxidation Rate (g/m2/d)



# 100% oxidation flux, Zero emission flux maximum oxidation capacity 

# AN ALTERNATIVE TO A SINGLE VALUE: OXIDA TION A S 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 exp ressed 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 po rtion of the methane delivered to them, potentially oxidizing 95 to 100 percent (Humer and Lechner, 1999, 2001a, Huber

Humer 2008; Powelson et al., 2006, 2007; Kjeldsen et al., 1997). As out

- flux rates increase, the percent oxidation decreases and the me thanotrophs 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 oxid ation by (Abichou et al., 2010), demonstrates

that at lower methane fluxes

, oxidation rates are equal to the methane loadi ng 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.

T his 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 rat e fails to keep pace, and the percent oxidation decreases.

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

* D emonstrating 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 t his 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 r ight 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 methan e 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 alternati ve 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 g as 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 r eflects 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 wo rking 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 - 2 

## day - 1 

## , the best value for methane oxidation is 38.4 percent, for results between 10 and 70 grams methane m 2 

## day - 1 

## the best value is 27.4 percent, and for covers with emissions above 70 grams methane m 2 

## 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 CH 4 m -2 d -1methane oxidation g CH4m-2d-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 CH 4 

### m - 2 

### d

- 1 

### placing it at the high

end of tier t wo.



## 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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Abichou, T., Chanton, J., Powelson, D., Fleiger, J., Escoriaza, S., Lei, Y., and Stern, J. 2006. Methane flux and oxidation at two types of intermediate landfill covers, Waste Management 26: 1305

- 1312. Abichou, T., Johnson, T., Mahieu, K., Chanton, J., Romdhane, M., and Mansouri, I. 2010. Developing a Design Approach to Reduce Methane Emis s ions from California Landfills, Geotechnical Special Publication No. 199, eds. Fratta, D., Muhunthan, B., and Puppala, A., ASCE, Baltimore, MD USA. Abichou, T., K. Mahieu, J. Chanton. M. Romdhane and I Mansoure. 2011a. Scaling methane oxidation: from laboratory incubation experiments to landfill cover field 987. Waste Management, 31, 978

- 987. Abichou T. J. Clark and J. Chanton. 2011b. Reporting central tendencies of chamber measured surface emission and oxidation. Waste Management, 31, 1002

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8251

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content, te mperature and nitrogen

- turnover . Journal of Environmental Quality 25 (1), 178

- 183. Boeckx, P., Van Cleem put, O., Villaralvo, I., 1996. Methane emission from a landfill and the methane oxidisin g capaci ty of its covering soil . Soil Biology and Biochemistry 28, 1397

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- 277. Bogner, J. E., Spokas, K.A., Burton, E.A., 1997b. “Kinetics of Methane Oxidation in a Landfill Cover Soil: Temporal Variations, a Whole

- Landfill Oxidation Experiment, and Modeling of Net CH4 Emissions”. Environmental Science and Technology 31, 2504

- 2514. Bogner, J., K. S pokas, and J. 2011. Chanton. Seasonal Greenhouse Gas Emissions (CH4, CO2, N2O) from Engineered Landfills: Daily, Intermediate, and Final California Cover Soils. 2011. Journal of Environmental Quality, 40:1010

– 1020 doi:10.2134/jeq2010.0407 Borjesson, G., Chanton, J., Svensson, B.H., 2001. Methane oxidation in two Swedish landfill covers measured with

carbon

- 13 and carbon

- 12 isotope ratios . Journal of Environmental Quality 30, 376

- 386. Borjesson, G., Samuelsson, J., and Chanton, J. 2007. Methane oxidation i n Swedish landfills quantified with the stable carbon isotope technique in combination with an optical method for emitted methane, Environmental Science & Technology 41: 6684

- 6690. Chanton, J.P., C.M. Rutkowski and B. M. Mosher. 1999. Quantifying methane oxidation from landfills using stable isotope analysis of downwind plumes. Environmental Science and Technology, 33, 3755

- 3760. Chanton, J., Liptay, K., 2000. Seasonal variation in methane oxidation in landfill cover soils as determined by an in

situ stab le isotope technique. Global Biogeochemical Cycles 14, 51

- 60. Chanton, J.P., Powelson, D.K., Abichou, T., and Hater, G. 2008. Improved field methods to quantify methane oxidation in landfill cover materials using stable carbon isotopes, Environmental Scien ce & Technology 42:

665

- 670 Chanton, J. P. , D. K. Powelson, R. B. Green. 2009. Methane Oxidation in Landfill Cover Soils, is a 10% Default Value Reasonable? J. Environ. Qual. 38:654

– 663. Chanton, J., T. Abichou, C. Langford, G. Hater, R. Green, D. Goldsmi th and N. Swan. 2011a. Landfill Methane Oxidation Across Climate Types in the U.S. Environmental Science Technology. 45 (1): 313

- 319. Chanton, J.P., T. Abichou, C. Langford, K. Spokas, G. Hater, C.D. Goldsmith, and M. Barlaz. 2011b. Observations

on the Me thane Oxidation Capacity of Landfill Soils, Waste Management, 31 (2011) 914

– 925 Christophersen, M., Linderød, L., Jensen, P.E., Kjeldsen, P., 2000. Methane Oxidation at Low Temperatures in Soil Exposed to Landfill Gas. Journal of Environmental Quality 29, 1989

- 1997. Christophersen, M., Kjeldsen, P., Holst, H., Chanton, J. 2001. Lateral Gas Transport in Soil adjacent to an Old Landfill: Factors Governing Emissions and Methane Oxidation. Waste Management and Research. 19, 595

- 612. Czepiel, P.M., Mosher, B., Crill, P.M., and Harriss, R.C. 1996a. Quantifying the effect of oxidation on landfill methane emissions. J. Geophysical Research 101 (D11):16721

- 16729.

### SWICS Methane Oxidization Addendum 2012



## 19 Czepiel, P.M., Mosher, B., Harriss, R.C., Shorter, J.H., McManus, J.B., Kolb, C.E., Alwine, E., and Lamb, B.K. 1996b. Landfill methane emissions measured by enclosure and atmospheric tracer methods. J. Geophysical

Research 101:16711

- 16719. Dever, S.A. GE.Swarbrick and R.M. Stuetz. Passive drainage and biofiltration of landfill gas. Results of an

Austr alian field trial. Waste Management, 31, 1029

- 1040. De Visscher, A., Thomas, D., Boeckx, P., Van Cleemput O., 1999. Methane Oxidation in Simulated Landfill Cover Soil Environments. Environmental Science and Technology 33, 1854

- 1859.

Gebert , J., I.U. Rower, H. Scharff, C. D. Roncato and A.R. Cabral. Can soil gas profiles be used to assess microbial methane oxidation in landfill covers. Waste Manaagement 31, 987

- 986. Hilger, H.A., Wollum, A.G., and Barlaz, M.A. 2000. Landfill methane oxidat ion response to vegetation, fertilization, and liming. J. Environmental Quality 29: 324

- 334

. Humer, M., Lechner, P., 1999. Alternative approach to the elimination of greenhouse gases from old landfills. Waste Management and Research, 17, 443

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Humer, M. & Lechner, P. 2001a. Design of a landfill cover layer to enhance methane oxidation. results from a two year field investigation. In: Christensen, T. H., Cossu, R. & Stegmann, R. (eds.) Proc. SARDINIA 2001

– Eighth International Waste Management and Landfi ll Symposium, Margherita di Pula, Italy, Vol. II Leachate and Landfill Gas, p. 541 f., Published by CISA Environmental Sanitary Engineering Centre, Cagliari, Italy. http://p eople.engr.ncsu.edu/barlaz/resources/biocover%20hummer.pdf

Huber

- Humer, M., J. Gebert, and H. Hilger. 2008. Biotic systems to mitigate landfill methane emissions. Water Management Research 26, 33

- 46. DOI: 10.1177/0734242X07087977

Huber

- Humer, M., J. Ti ntner, K. Bohn and P. Lechner. 2011. Scrutinizing compost properties and their impact on methane oxidation efficiency. Waste Management 31, 871

- 878. IPCC 2006. Guidelines for national greenhouse gas inventories. http://www.ipcc

- nggip.iges.or.jp/public/2006gl/index.html IPCC 2000. Good practice guidance and uncertainty management in national greenhouse gas inventories. http://www.ipcc

- nggip.iges.or.jp/public/gp/gpg

- bgp.html Jung, Y. P.T. Imhoff, d. Augenstein, and R. Yazdani. 2011. Mitigating methane emissions and air intrusion in heterogeneous landfills with a high permeability layer. Waste Managem ent, 31, 1049

- 1059. Kjeldsen, P., A. Dalager, and K. Broholm 1997. Attenuation of methane and nonmethane organic compounds in landfill gas affected soils. J. Air Waste Manage. Assoc. 47:1268

- 1275. Kightley, D., Nedwell, D.B., Cooper, M., 1995. Capacity for methane oxidation in landfill cover soils measured in laboratory

- scale soil microcosms. Applied and Environmental Microbiology 61, 592

- 610. Liptay, K., Chanton, J., Czepiel, P., Mosher, B. 1998. Use of stable isotopes to determine methane oxidation in landfill cover soils. Journal of Geophysical Research 103, 8243

- 8250. Pawlowska,M., A. Rozej, and W. Stepniewski. 2011. The effect of bed properties on methane removal in and aerated biofilter. Model studies. Waste Management 31, 903

- 913. Pedersen, G.B . C. Scheutz, and P. Kjeldsen. 2011. Availability and properties of materials for the Fakselandfill biocover. Waste Management 31, 884

- 894. Powelson, D., Chanton, J.

, Abichou, T., and Morales, J. 2006 Methane Oxidation in Compost and Water Spreading Biofilters, Waste Management Research , 29, 1

- 9. Powelson, D.K., Chanton, J.P., and Abichou, T. 2007. Methane oxidation in biofilters measured by mass

- balance and stable isotope methods. Environ. Sci. Technol. 41: 620

- 625. Rachor, I, J.Gebert, A. Grongrof t and EmM. Pfeiffer. 2011. Assessment of the methane oxidation capacity of compacted soils intended for use as landfill cover materials. Waste Management, 31, p 833

- 842

. Scheutz, C., Bogner, J., Chanton, J., Blake, D., Morcet, M., Kjeldsen, P., 2003. Comparative Oxidation and Net

Emissions of Methane and Selected Non

- Methane Organic Compounds in Landfill Cover Soils. Environmental Science and Technology, 37, 5150

- 5158. Scheutz, C., and Kjeldsen, P. 2003. Capacity for biodegradation of CFCs and HCFCs in a methane oxidative

counter

- gradient laboratory system simulating landfill soil covers, Environ. Sci. Technol. 37: 5143

- 5149. Scheutz, C., Bogner, J., De Visscher, A., Gebert, J., Hilger, H., Huber

- Humer, M., Kjeldsen, P., and Spokas, K.

2009. Processes a nd technologies for mitigation of landfill gas emissions by microbial methane oxidation. Critical Reviews in Environmental Science & Technology. Scheutz, C., A. Pedicone, G.B. Pedersen and P. Kjeldsen. 2011. Evaluation of respiration in compost landfill biocovers intended form methane oxidation. Waste Management 31, 895

- 903.

### SWICS Methane Oxidization Addendum 2012



## 20 Spokas, K., Bogner, J. and Chanton, J. 2011. A process

- based inventory model for landfill CH4 emissions inclusive of seasonal soil microclimate and CH4 oxidation Journal of Geoph ysical Research, Biogeosciences, VOL. 116, G04017, doi:10.1029/2011JG001741. Stern, J.C., Chanton, J., Abichou, T., Powelson, D., Yuan, L., Escoriza, S., and Bogner, J. 2007. Use of a biologically active cover to reduce landfill methane emissions and enhan ce methane oxidation, Waste Management 27: 1248

- 1258. SWICS, 2009. Current MSW Industry Position and State

- of

- the

- Practice on LFG Collection Efficiency, Methane Oxidation, and Carbon Sequestration in Landfills. Solid Waste Industry for Climate Solutions (S WICS), prepared by SCS Engineers. Version 2.2, January 2009. http://www.scsengineers.com/Papers/Sullivan_SWICS_White_Paper_Version_2.2_Final.pdf

US

- EPA 2006 . OTM10. Final ORS Protocol, June 14, 2006. http://www.epa.gov/ttn/emc/prelim/otm10.pdf
USEPA, 2004. Direct Emissions from Landfilling Municipal Solid Waste, U.S. Environmental Protection Age ncy, Washington, D.C. USEPA, 1998. Greenhouse Gas Emissions From Management of Selected Materials in Municipal Solid Waste.

E PA530

- R

- 98

- 013, September 1998. Visvanathan, C., Pokhrel, D., Cheimchaisri, W., Hettiaratchi, J.P.A., and Wu, J.S., 1999. Methan otrophic activities in tropical landfill cover soils: effects of temperature, moisture content and methane concentration. Waste Management & Research 17: 313

- 323. Wilshusen, J. H., Hettiaratchi, J. P. A., Stein, V. B., 2004. Long

- term behaviour of passively aerated compost methanotrophic biofilter columns. Waste Management 24, 643

- 653. Whalen, S.C., Reeburgh, W.S., Sandbeck, K.A., 1990. Rapid methane oxidation in a landfill cover soil. Applied and Environmental Microbiology 56, 3405

- 3411.

### SWICS Methane Oxidization Addendum 2012



## 21 Tabl e 2 F ootnotes:

Abichou et al., 2006. Oxidation rates (J

ox 

### ) calculated from emission fluxes (J out 

### , their Table 1) and oxidation fractions (f

ox 

### , 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/squa re 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

, , c rel b rel a rel 

## s s s + = (f2)

where s rel 

### 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 δ 13 

### C . Bogner et al., 1997. Oxidation estimated from their Fig. 3 for two ranges of initial CH 4 

### concentration: 135 to 145

ppm v 

### 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

1 

## + + = s s s avg 

### (f3)

where s avg 

### is the standard deviation of the average and s 1 

### , s 2 

### , 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 CH 4 

### emiss ion 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 δ 13 

### C SEs. Subsurface samples taken from 5 to 10 cm depth with probes.

Chanton et al. 2011 . Isotope study of 20 landfills with 37 seasonal samp ling 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 e t 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 assumi ng bulk density of 1.7 g cm 3 

### . 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 err or 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 replicate s; 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. Oxidati on estimated from their Fig. 5 at inlet flow rates of 0.24 and 3.18 m 3 

### m - 2 

### d
- 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 V

max 

### 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.