## RTI International 

## 1

Date: June 17 , 201 5

To: Rachel Schmeltz, EPA

From: Kate Bronstein, Meaghan McGrath, Jeff Coburn, RTI Inter national

Subject: Review of Oxidation Studies and Associated Cover Depth in the Peer

Reviewed Literature – Revised Memorandum



# 1. Purpose

This memorandum documents a review of the fraction of land fill methane oxidation presented in the peerreviewed literature and associated landfill soil cover depths.



# 2. Background

As methane generated in the landfill flows up through a landfi ll’s cover soil, a fraction of that methane will be
oxidized or metabolized by methanotrophic bacteria near th e soil surface. The relative amount of methane
removed from the landfill gas stream as the gas passes th rough the soil surface layer is termed the fraction
oxidized or oxidation fraction. The fraction oxidized depend s on a number of factors including:

• The flow velocity of landfill gas, or the methane flux, t hrough the soil surface (higher flux rates means
lower residence times in the aerobic soil layer and less oxidation),

• The porosity of the soil layer (greater porosity leads t o more air ingress and a thicker aerobic soil layer,
which leads to more oxidation),

• The number and types of microorganisms in the surface s oil layer, and

• The soil surface temperature and moisture, which may inc rease or inhibit microbial activity.

For the first three reporting years under 40 CFR Part 98 S ubpart HH of the EPA’s Greenhouse Gas Reporting
Program, owners and operators of municipal solid waste ( MSW) landfills were required to use an oxidation
fraction of 10 percent when estimating methane emissions f rom MSW landfills. Industry representatives
commented that the 10 percent oxidation fraction was too l ow and that many landfills have much higher
oxidation fractions as shown in the recent published litera ture. Additionally, numerous U.S. landfills with
active gas collection systems and clay soil or ‘‘other soil mixture’’ covers have been tested in the past decade to
estimate the oxidation fraction. The 10 percent default valu e is based off of a study 1 

## conducted in the early
nineties (Czepiel et al., 1996).

Industry representatives compiled data from peer-reviewed studies and evaluated soil oxidation fractions
(SWICS, 2012) to support their statement and provide options for using the data to estimate the oxidation

1 

## Czepiel, P. M., B. Mosher, P. M. Crill, and R. C. Ha rriss (1996), Quantifying the effect of oxidation on landfill methane emissions, J. Geophys. Res., 101(D11), 16721–16729, doi:10.1029/96JD00222.

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## 2 fraction for MSW landfills reporting under Subpart HH. T hese options, a comparison of methane emissions that
would be reported using these options based on methane flux da ta provided by industry representatives, and
recommendations for selecting a specific option for inclusion in Subpart HH to replace the current 10 percent
default oxidation fraction requirement are documented in a memorandum dated December 7, 2012 (see Docket
ID No. EPA–HQ–OAR–2012–0934). Based on the analysis documented in t he aforementioned memorandum,
the following changes to the oxidation fractions were proposed on April 2, 2013 (78 FR 19802):

• Three different default oxidation fractions depending on the methane flux bin (see Table 1 ) were
proposed to provide a more realistic estimate of the role of methane oxidation in the surface soil on the
methane emissions than the single default oxidation fracti on.

o For cases where the methane flux is projected to be high (g reater than 70 grams/m 2 

## /day), the
default oxidation fraction remains as 10 percent.

o For cases where the methane flux is projected to be low (le ss than 10 grams/m 2 

## /day), the
default proposed oxidation fraction is 35 percent.

o For cases with moderate methane flux rates (10 to 70 grams/m 2 

## /day), the proposed default
oxidation fraction is 25 percent.

• A calculation method to determine the methane flux rate to be used for determining the oxidation
fraction when Equations HH–5, HH–6, HH–7, or HH–8 are used was also proposed.

Table 1. Proposed Table HH-4 to Subpart HH of Part 98—Landfill Methane Oxidation Fractions



## If your methane flux rate for the reporting year is: Use this landfill methane

oxidation fraction: Less than 10 grams per square meter per day (g/m 2 

## /d) 0.35 10 to 70 g/m 2



## /d 0.25 Greater than 70 g/m 2 

## /d 0.10

The proposed changes to the methane oxidation fractions did not include cover depth requirements. The need
for a cover depth requirement resulted from a public comment ( Center for a Competitive Waste Industry
[CCWI]) in response to the definition of the methane flux rat e, which is defined as a footnote to Table HH-4 as
the mass flow rate of methane per unit area at the bott om of the surface soil prior to any oxidation. The
inclusion of the ‘bottom of the surface soil’ phrase in thi s definition triggered a comment regarding the need for
a defined soil cover depth and specifically noted that land fills with geomembrane covers and no cover soil
should be assigned an oxidation fraction of zero. CCWI also noted that “...oxidation only occurs in landfill
covers that are comprised only of soil (with the necessary de pth, porosity, temperature and microbes), and not
through composite covers that include a low permeable geomem brane.”

The 24 inch soil cover depth requirement was a logical outgrow th of these comments. To address these
comments, peer-reviewed literature, as synthesized in SWI CS 2012, was reviewed. The soil cover depths
reported in the studies on which the higher oxidation fracti ons were based had soil covers of at least 24 inches.
If one assumes the measurements were taken at representative areas of each landfill, it can also be assumed that
the soil cover depths reported at the measurement locations were similar to the majority (i.e., > 50 percent) of
the landfill surface. Therefore, a soil depth of 24 inches over the majority of the landfill was selected as the
basis for using the higher oxidation rates. An industry expert was also consulted and confirmed 24 inches of
intermediate cover was typical industry practice. Nonetheless , several of these studies indicated that soil
oxidation tends to occur in the top 12 inches of the soil cover . Considering these data, we determined it would

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## 3 be appropriate to allow landfills with geomembrane covers to use the 0.10 oxidation fraction. Releases of
surficial landfill gas from landfills with geomembrane covers are expected to be isolated to areas where leaks
from the cover may occur (e.g., seams or tears). We expect the flux rate through the soil to be high (in those
areas where flux occurs); therefore, landfills with soil c over over a geomembrane cover may only use the 0.10

oxidation factor.

Based on public comments received and our review of the availa ble published literature, the following
oxidation fraction values and soil cover depths were promu lgated (78 FR. at 71925, see Table 2 ).

Table 2. Promulgated Table HH-4 to Subpart HH of Part 98—Landfill Methane Oxidation Fractions



## Under these conditions: Use this landfill methane

oxidation fraction:

I. For all reporting years prior to the 2013 reporting year

C1: For all landfills regardless of cover type or metha ne flux 0.10

II. For the 2013 reporting year and all subsequent years

C2: For landfills that have a geomembrane (synthetic) cover w ith less than 12 inches of cover soil for the majority of the landfill area containing waste 0.0

C3: For landfills that do not meet the conditions in C2 above , and for which you elect not to determine methane flux 0.10

C4: For landfills that do not meet the conditions in C2 above and that do not have a soil cover of at least 24 inches for a majority of the landfill area containing waste 0.10

C5: For landfills that have a soil cover of at least 24 i nches for a majority of the landfill area containing waste and for which the methane flux rate is less than 10 grams per square meter per day (g/m 2 

## /d) 0.35

C6: For landfills that have a soil cover of at least 24 i nches for a majority of the landfill area containing waste and for which the methane flux rate is 10 to 70 g/m 2 

## /d 0.25

C7: For landfills that have a soil cover of at least 24 inches for a majori ty of the landfill area containing waste and for which the methane flux rate is greater than 70 g/m 2



## /d 0.10



# 3. Summary of the Petition for Reconsideration

Waste Management (WM) petitioned EPA for reconsideration in light of the revision to the oxidation fraction made to the rule affecting Subpart HH for MSW Landfills 2 

## . The petition states the soil cover requirement of 24 inches over the majority of the landfill containing waste wil l needlessly limit the number of reporters who can use alternative methane oxidation fractions, and thus mor e reporters will be relegated to the default 10 percent

default oxidation factor.

2 

## See Docket I.D. EPA-HQ-OAR-2012-0934 in response to the 2013 Revi sions to Greenhouse Gas Reporting Rule and Final Confidentiality Determinations for New or Substa ntially Revised Data Elements; Proposed Rule, 78 Fed. Reg. 19802-19877, 19825 (April 2, 2013).

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## 4 The following is a brief summary of the arguments in the petition:

• The 24 inch soil requirement is arbitrary and not based on sound science (no correlation between depth
and methane oxidation).

• The oxidation issue was not raised in proposal comments r eceived by the Center for Competitive Waste
Industries and Covanta on which the change was based; these comments do not specifically mention
soil depth or provide data for a logical outgrowth to 24 inche s.

• A soil cover requirement of 24 inches is not a logical outgrowt h of comments received and peerreviewed literature and is “so distant from the Propo sed Rule that WM could not have anticipated its

inclusion in the Final Rule.”

• The majority of WM landfills will be precluded from using the higher bins of methane oxidation and
will suffer the burden of over-reporting emissions because the 24 inch soil cover requirement cannot be

met.

The petitioner requests EPA to convene a reconsideration proc eeding to fully evaluate and correct this technical revision by either:

• Removing the 24-inch soil cover requirements altogether OR

• Allowing reporters to use intermediate cover as the soil c over requirement, which would effectively
require a 12-inch soil cover requirement. The petitioner not es that 27 states in which ~77% of MSW
landfills are located have intermediate cover requiremen ts of 12 inches, either exclusive or inclusive of
the federally mandated 6 inches of daily cover.



# 4. Methods

Peer-reviewed literature was reviewed to tally all me ntion of soil cover depth and use of direct quotes in the WM petition. The following steps were completed under this ta sk:

• Gathered copies of all studies explicitly mentioned by WM in their petition;

• Compiled information on the fraction of methane oxidized, soil cover type, and/or depth in the studies
included in the WM petition as well as the studies include d in SWICS 2012;

• Reviewed each study to verify that all quotations cited in the petition were direct quotes; and

• Determined if any additional information in the cited studi es contradicts or supports the quotes used in
the petition.



# 5. Findings

5.1 Soil Cover Depth Included in Reviewed Methane Oxida tion Studies

• Multiple studies give reference to and/or support the Czepi el et al. (1996) study which estimated a 10%
methane oxidation fraction for any given landfill throughout the entire year, considering higher
methane oxidation during warmer summer months and lower rat es during winter.

• Other studies (e.g., Chanton et al., 2011) argue specifical ly for a higher default methane oxidation in
landfills with gas collection, using their data to support t heir claims (700+ measurements, etc.).

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## 5 • Temperature (in terms of seasonal variability) is consi stently presented as a significant variable for

methane oxidation fraction at landfills.

• All studies include soil characteristic data (e.g., mois ture content, soil type, pH, soil cover
depth/thickness). While soil cover depths were neither presented in every study reviewed, nor explicitly
mentioned as an influencing variable in every study reviewed , all studies were conducted at a landfill
or a simulated landfill environment with some depth of soil c over. It can therefore be concluded that
some amount of soil cover is important for methane oxidat ion to occur; however the studies do not
allow for a conclusion on the optimum depth of that soil c over. Two recent studies, Bogner et al.
(2011) and Abichou et al. (2006) note a relationship between cove r thickness and methane oxidation:

o Bogner et al. (2011) note that landfill methane emissions ar e reduced by three major
mechanisms, one of which is “the thickness and physical properties of engineered cover
materials” (p. 1010). They also note that “thicker cover mat erials retard transport and increase
retention times to facilitate oxidation.” (p. 1010).

o Abichou et al. (2006) investigated methane flux and oxidation a t two types of intermediate
landfill covers and found that methane oxidation was higher at the site with a thicker (45-cm or
17.7 in.) cover over 7-year old waste compared to a 15-cm (5.9 in. ) cover over 1-year old
waste. The average flux for both landfill covers were in the intermediate range (22 g/m 2 

## /d for
the thicker cover and 54 g/m 2 

## /d for the thinner cover. The authors note “The mean percent
oxidation was significantly greater (25%) at the thick c over relative to the thin cover (14%).” (p. 1305).

• 27 peer-reviewed studies, included in either or both the SWIC S 2012 Addendum or in RTI 2011, were
reviewed for soil cover depths in relation to the oxidati on fraction. From these studies, a total of 90
measurements were included, but only 63 data points were considered (including 49 field
measurements and 14 column measurements) for the purpose of this memorandum. Only data points
where both an oxidation fraction and a soil cover depth were presented were included for the purposes

of this memorandum. Table A-1 summarizes key data from all 27 peer-reviewed studies, inc luding the
soil cover type and depth and the fraction of oxidized meth ane.

• 52 of the 61 data points (or 85%) gathered from the studies that explicitly mentioned a cover depth and
an oxidation fraction, reported a cover depth of 24 inches or above. When only data points from field
studies are included (49 field data points), 89% of data poi nts were associated with a cover depth of 24
inches or above. Regardless of the column or field measure ment, all studies reviewed were conducted,
or can be assumed, to have been conducted at a landfill o r landfill-type environment (for column
studies) with a cover.

• The Wilshusen et al. (2004) column study was performed on com post comprised of leaf litter and
manure. For the purpose of this memorandum, this study data was not included as we consider it an
emerging cover type and is not commonplace at closed or ope rational MSW landfills.

• Fifteen studies, including the Wilshusen et al. (2004) study, were cited in the WM petition (see Table

3 ). Five were column studies and the rest field studies. If the Wilshusen et al. (2004) study is not

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## 6 considered, 13 of the 14 remaining studies collected measurements at one or more locations with s oil
cover depth meeting or exceeding 24 inches.

• Eleven studies (Cabral et al., 2010; Chanton et al., 2008; Geb ert et al., 2011a and 2011b; Huber-Humor
et al., 2009, Knightley et al., 1995; Rachor et al., 2011; Sche utz et al., 2009; Schroth et al., 2012;
Spokas and Bogner, 2011; Wilshusen, et al., 2004) measured methane and/or oxygen profiles in the
surface cover soil. While the cover soils generally exceede d 24 inches in these studies and only three

of the studies were conducted in the field, most of the m ethane oxidation appears to occur in the top 12
to 15 inches (30 to 40 cm) of the cover soil.

• Two studies (Liptay et al., 1998 and Chanton and Liptay, 2000) n oted that methane flux in areas near
passive vent pipes were much smaller than in other areas of the landfill.

Table 3. Soil Cover Depth and Landfill Status of La ndfills in the Peer-Reviewed Studies Included in th e Petition Author(s) Field or

Column Open/Closed Cover Soil Depth (in) Fraction

Oxidized Notes

Barlaz et al. (2004) Field No explicit
mention • 39 (soil)

• 45 (biocover) • 0.21

• 0.54 Biocover consisted

of 0.15 m thick clay layer over the waste, followed by 0.15 m of tire chips, then 1 m of yard waste compost Bogner et al. (1997) Column Closed (final cover 1980s) • 49 • Not reported

Chanton and Liptay (2000) Field Closed • 43

• 39 • 0.26

• 0.14 Samples taken from

3-15cm below the
surface

Chanton et al. (2008) Field No explicit
mention • Site 1: 29

(additional biocover)

• Site 1: 51 (additional biocover)

• Site 2: 6 (deep biocover)

• Site 2: 35 (deep biocover)

• Site 2: 23 (shallow biocover) • Site 1: 0.40

• Site 1: 0.29

• Site 2: 0.08

• Site 2: 0.12

• Site 2: -0.01 Measurements

taken from multiple locations; Site 1
sites had additional biocover; Site 2 sites had deep biocover
and shallow cover

Chanton, et al. (2011) Field No explicit
mention • 12-48 • 0.06-0.82 Range of cover depth provided
Christopherson et al. (2001) Field Closed • 39 • 0.28

• 0.89

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## 7 Author(s) Field or

Column Open/Closed Cover Soil Depth (in) Fraction

Oxidized Notes

Czepiel et al. (1996) Field No explicit
mention • 39-79 • 0.1 Range of cover depth provided

De Visscher et al. (1999) Column Closed and/or
Abandoned • 24 • 0.61+

• 0.65 Cover depth as

presented in SWICS

2012
Hilger et al. (2000) Column Closed • 12 • 0.21 Cover depth as presented in SWICS

2012 Kightley et al. (1995) Column No explicit
mention • 35 • 0.40

• 0.41

• 0.61

Liptay et al. (1998) Field No explicit
mention • NR • 0.0-0.68 Samples taken from
3-15cm below the
surface

Scheutz and Kjeldsen (2003) Column No explicit
mention • 35 • 0.96+ Aerobic experiments sampled at 15-20 cm depth; anaerobic experiments sampled at 50-60 cm depth
Stern et al. (2007) Field Closed • 39-69 • 0.19-0.38 Range of cover depth provided

Wilshusen et al. (2004) Column NA • NA • 0.19 This study was
conducted on compost and
manure and is atypical of landfill cover practice, and
is not a representative
choice for this analysis.
Goldsmith et al. (2012) Field No explicit
mention • 0 (no cover)

• 6-12 (temporary cover)

• 24-47 (intermediate cover)

• 39-79 (final cover) • Not reported Measurements taken from multiple
landfills across the
United States.

Methane fluxes are provided, but presented by
area/state with no relationship between
which

measurements were taken at which cover depth NR = not reported NA = Not applicable

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## 8 

# 5.2 Citations in the Petition

Within their petition to EPA, WM references a total of 15 peer-reviewed studies to support their central
argument that soil depth is not a significant factor infl uencing methane oxidation at MSW landfills. The studies
are incorporated as footnotes in the petition to support t hree different statements. These statements are
presented at the beginning of Sections 5.2.1 through 5.2.3 of this memorandum, followed by a brief analysis of
the quoted text and study presented in the petition’s footnot es. These brief analyses indicate whether the
information presented throughout the study does or does not suppor t the quote used in the petition.

In general, all quotations taken from the literature and pr esented in the petition were direct quotations. Only 3
citations were not direct quotations (Chanton et al., 200 8 in response to quote in Section 5.2.2 in this

memorandum; and Chanton et al., 2011 and Goldsmith et al., 2012 in response to quote in 5.2.3 in this
memorandum), however these quotes accurately described the f igures and/or tables to which they were
referencing.

Multiple studies indicate the complexity of methane oxida tion through soil in the landfill setting (Stern et al.,
2007; De Visscher et al., 1999; Scheutz and Kjeldsen, 2003) and al l studies that observed landfill flux behavior
over the course of multiple seasons found a similar relations hip between methane oxidation and temperature:

oxidation increases in warmer, summer months and decreas es in colder, winter months. In addition to
temperature, Bogner et al. (1997) state that methane oxidat ion is important, at times, in deeper landfill settings
as a result of the relationship between different species of bacteria in the landfill layers.

Three studies show evidence of a 10% methane oxidation fracti on (Liptay et al., 1998; Barlaz et al., 2004;
Czepiel et al., 1996) when all seasonal averaging is taken i nto account at a site, however, Barlaz et al. (2004) do
note that these values were obtained at specific landfill s, and thus may not be applicable to all landfills.

5.2.1 Page 17, paragraph 2: “Additionally, more detailed review of the studies referenced in the 2012 SWICS Addendum does not support the conclusion that soil depth is a significant factor influencing methane oxidation.”

Barlaz et al. (2004): “Several factors have been shown to influence the extent of CH 4 

## oxidation in landfill soil
cover soils, including CH 4 

## and O

2 

## concentrations, temperature, moisture content, soil composition, moistur e holding capacity, pH and nutrient content.”

• The study begins by referencing the aforementioned factors as a probable cause of influence to CH 4 

## oxidation in landfill cover soils, but later concludes that “there was not significant correlation between
either ambient temperature or pressure and CH 4 

## flux” (pg. 4895) in laboratory scale experiments
conducted during the course of the study. The study continues t o state that “there was not a significant
correlation between either temperature or pressure change and the measured flux” (pg. 4895). In terms
of direct mention of methane oxidation values, the study notes that “when annual CH 4 

## oxidation is
considered on a seasonally averaged basis, values of 10% an d 14% have been estimated for soil covers
in the Northeast and Florida, respectively” (pg. 4891). The authors note these values are site-specific.
Barlaz et al. (2004) state that 21% of the methane was oxi dized in the soil cover study area (pg. 4898),
and the study area was covered by 100-cm (~39-in) of clay (pg . 4892).

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## 9 Bogner et al. (1997): “Limitations on physical transport become major con trols in the field, where relative
rates of CH

4 

## and O 2 

## transport to a given depth are restricted by rates of methanogenesis below and by O 2 

## transport from atmospheric sources above. Other factors that directl y control methanotrophic microbial
activity in the field include temperature, moisture, organic carbon c ontent, available nutrients, and predation
by or competition with other soil microorganisms.”



# • Bogner et al. (1997) note that “model inputs [in the study] were limited to the generalized site geometry
for portions of each site (length, width, depth, and soil c over thickness), mean values for soil moisture
and gas-filled porosity, and the soil gas profiles (geom etric mean) through the cover material” (pg. 2511) with the soil cover thickness consisting of silty clay “ approximately 100 cm thick overlain by
topsoil...approximately 25cm thick.” (pg. 2505) Soil depth was not spe cifically listed as an influencing
factor for methane oxidation, however all model outputs for th e study were based off of this 125cm

total soil cover.

Chanton et al. (2000): “in the landfill we studied, temperature was the main factor in controlling methane
oxidation at specific sites (Figures 8a and 8b)” and that “methane oxidatio n occurs in the outer rind of the
landfill and is subject to environmental temperature fluctuations whic h cause rates to be greater in summer and

lesser in winter.”

• Results from this study reveal a large difference betwee n methane oxidation rates during winter (3-5%
oxidation) and summer (maximum of 43 ± 10% in July) that are verified in the cited quotation (pg. 57).
Chanton et al. (2000) conclude that the seasonally integrate d value for methane oxidation for areas of
the landfill covered with mulch/topsoil was 26 ± 4% of the to tal methane oxidation rate, while for clay
soil it was only 14 ± 2% with the overall average of both soil types being 20 ± 3% (pg. 57). Soil
samples were taken from the top 15-cm of the cover soil, howeve r, the entirety of the final cover for the
sampled landfill was 109-cm where mulch/topsoil was still i n place and 100-cm where mulch/topsoil
had washed away.

Christopherson et al. (2001): “Methane oxidation is controlled by various environmental factors: temperature,
soil water content, nutrients, sub-strate, and oxygen concentrations.”

• Christopherson et al. (2001) generally support the notion of sea sonal variation in landfill gas flux with
higher fluxes in the summer months. The authors conclude that “from the figures discussed in the
previous sections it is difficult to identify the factors g overning lateral gas emission, but when
statistical analysis is used, it is possible to investig ate the influence of several factors at the same time.
... In general, the regression analysis on the summarised f luxes supports what is illustrated in the
figures in the previous sections: the fluxes depend on temper ature, and barometric pressure, and the
pressure gradient”, which is supported in WM’s citation. (pg. 605)

• The study also notes that “the concentrations of landfill gas and the soil moisture content in the upper
part of the soil profile have significant influence on the fluxes” (pg 605), however it is once again
important to note that the soil studied was taken from a landfill with a final cover of 100-cm (80-cm sand and 20-cm mould) (pg. 596).

Hilger et al. (2000): “Some of the factors that influence microbial C H 4 

## oxidation in landfills include climate variables such as moisture and temperature, as well as CH 4 

## concentrations, soil type, and pH.”

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## 10 • The Hilger study does not contain any information regarding t he soil cover of the landfill from which
fresh core samples were taken (the Renaissance Park l andfill in Charlotte, NC), however the study does

indicate that the landfill is closed and has since been converted into recreational fields. (pg. 458) The
study findings support the importance of the cited factors ( temperature, CH 4 

## concentration, etc.) on
methane oxidation and microbial activity in landfills.

Kightley et al. (1995): “In conclusion, our data show that soil microbial community adapts rapidly to the presence of elevated CH 4 

## concentrations and can effectively reduce emissions of CH 4 

## from the surface of landfill soil. The capacity for CH 4 

## oxidation in soil is related to the depth of O 2 

## penetration and to the nutrient status of the soil, which may regulate the extent to which the met hanotrophic community can develop.”

• This study permeated CH 4 

## into four landfill soil core samples (in triplicate wi th a control) measuring 1-
m by 15-cm and packed to a depth of 90-cm (p. 592). Three soil ty pes (minus any turf) were collected
from the upper 15-cm of various landfills and were sieved th rough a 20-mm mesh (p. 593). The soil

cores were saturated with CH 4 

## for a period of 6 months to provide “an estimate of the re lative biomass
of the methanotrophic population in the soil, as well as a n indication of the CH 4 

## -oxidizing capacity of each soil” (p. 593).

• “Measurement of the CH 4 

## oxidation potentials demonstrated that each of the soils had a capacity for
methanotrophy at most depths (Fig. 8), even extending into the anoxic layer.” (p. 596). We believe this
quote is referring to Figure 6 (and not Fig. 8), which s hows depth profiles for methane, oxygen,
nitrogen, and carbon dioxide for the coarse sand soil type af ter amending with various nutrient sources.
Figure 6 shows that 3 of the 4 coarse sand soil columns beca me anoxic at a depth of 30-cm, while the

4 th 

## (amended with NH 4 

## NO 3 

## ) was still aerobic at 80 cm deep. The authors suggest “th at it was the
development of a very active methanotroph community in the c oarse sand which rapidly removed O 2 

## and limited its penetration into this soil. In contrast, the development of equally active communities in
the other two soils was prevented by other factors such as nutrient limitation.” (p. 598).

• This study makes a link between soil type, depth, oxygen p enetration, nutrient status, and CH 4 

## oxidation.

Liptay et al. (1998): “Soil oxidation potential can change with factors such as temperature, pH and moisture

content.”

• In terms of quantifying soil oxidation, it is important t o note that Liptay et al. explicitly state that
“[their] study is consistent with the modeling results of C zepiel et al. (1996) that the best estimate for

the annual value for methane oxidation in the landfills con sidered is about 10%” (pg. 8243). Liptay et

al. later reiterate this statement and conclude that “ Czepiel et al. predicted that methane oxidation in the
soil cap of a New England landfill varied from 20 to 30% betwe en May and September, the period
during which our isotopic measurements were made. The season al pattern produced as a result of their
studies yielded an overall value of 10% over the whole year, a s oxidation rates are reduced
considerably at lower temperatures. Our isotopic determin ations of methane oxidation in the landfill
soil cap are fairly consistent with their model-predicted r esults and confirm the value determined in
their study.” (pg. 8248).

• The study does not give reference to a soil cover measurement , but does mention that “at least one area
of a working landfill is active, which means refuse is be ing dumped and covered by a minimum of 15-

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## 11 cm of soil or synthetic equivalent on a daily basis,” (pg . 8244) indicating a relationship between soil
cover depth and methane oxidation.

Stern et al. (2007): “Methane oxidation is controlled by several fac tors including soil temperature, moisture, and texture, as well as pH and nutrient content. Previous studies have shown seasonal variation in CH 4 

## oxidation, which is greater during warmer months. In addition, there appears to be optimum soil moisture for

CH 4 

## oxidation, 10-20% (w/w) at temperatures from 25 to 30 C...Soil compositi on is also an important parameter, as soil texture and grain size affect oxygen diffusion int o landfill cover soils. Coarser grained soils and porous mulch have been found to be superior to finer grained soils and clay s.”

• Stern et al. state that “conservative estimates put the average annual percent CH 4 

## oxidation at the Leon
County MSW landfill from 19% for untreated areas of the la ndfill to 38% for mulch treated
areas...Therefore, temperature is an important factor, but complex relationships exist between
temperature, moisture and CH 4 

## oxidizing capacity of cover materials, and their physical pro perties” (pg. 1255), which supports WM’s cited quote but also makes note of the intricate relationship between
environmental parameters at a landfill and how they interact with the soil and waste’s chemistry and
biology.

5.2.2 In regards to methane oxidation, Stern et al. (2007 ) note that their data, after and including June 29, indicate a mean oxidation of 14% for control cells with only soil cover (pg. 5146) which ranged in depth from 40 to 110-cm of cover (pg. 5144). “In fact, many of the studies conclude that methane oxidation primari ly occurs in the upper part of the cover, close to the surface, and several of the stu dies do not even calculate methane oxidation below a depth of 30 to 45 cm (15 to 18 in ches).” Pg. 17-18

Bogner et al. (1997): concluding that there is one group of microorganisms “that is continuously active in shallow landfill soils, which thus have the capacity for continuous CH 4 

## oxidation that rapidly responds to a wide range of dynamic CH 4 

## concentrations. The only exception would be during times of periodic surf ace saturation.”

“As shown by previous literature, rates of CH 4 

## oxidation are also dependent on temperature, moisture, and other variables. Nevertheless, in a well-aerated landfill soil ove r short time frames where a wide dynamic range of CH

4 

## oxidation rates is possible, the primary controlling variable appears to be CH 4 

## concentration and, secondarily, aeration status (O 2 

## availability).”

“Previous stable carbon isotopic measurements for deep landfill CH 4 

## below the cover materials, suggest that

CH 4 

## oxidation is also important, at least periodically, in deeper landfi ll settings.”

• WM’s selected quotes from the Bogner study are in referen ce to microbial activity in landfills, and how
there are generally two distinct groups of microorganisms whi ch influence methane oxidation through
the landfill cover soil. The third quote cited by WM from the Bogner study notes that methane
oxidation is important at times in deeper landfill set tings. Bogner et al. “postulate that the previously
described group (high CH 4 

## , low O 2 

## ) [in moderate to deeper landfill settings], or a third group able to
function very close to a lower limiting value for O 2 

## , may also be active at high CH 4 

## concentrations [in
deep landfills] (pg. 2510).

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## 12 Chanton et al. (2000): “Methane oxidation occurs in the outer rind of the landfill and is subject to environmental temperature fluctuations which cause rates to be greater i n summer and lesser in winter.”

• To reiterate from the previous section, this Chanton study r eveals a large difference between methane
oxidation rates during winter (3-5% oxidation) and summer (maximum of 43 ± 10% in July) (pg. 57).
Chanton et al. conclude that the seasonally integrated value for methane oxidation for areas of the
landfill covered with mulch/topsoil was 26 ± 4% of the tota l methane oxidation rate, while for clay soil
it was only 14 ± 2% with the overall average of both soil type s being 20 ± 3% (pg. 57). Soil samples
were taken only from the top 15-cm of the cover soil, however, t he entirety of the final cover for the
sampled landfill was 109-cm where mulch/topsoil was still i n place and 100-cm where mulch/topsoil
had washed away, which should not be ignored when consideri ng the complex behavior of landfill

soils.

Chanton et al. (2008): at Figure 1 (demonstrating that C-13 gets more posit ive between a depth of 20 and 60cm, which is indicative of methane oxidation)

• A review of Figure 1 on page 668 of this Chanton study reveals t hat the trend mentioned in WM’s
petition (C-13 getting more positive between a depth of 20 and 60-cm) can be further extended to a
depth of 80-cm, or in some cases, 100-cm. Total soil covers r anged from 73 to 130-cm (with biocover) in Site 1 of the study area and from 15 to 58-cm and 88-cm (sh allow and deep biocover, respectively)
in Site 4. Overall, Chanton et al. found the percent oxida tion to be 23± 3% for soil covers.

Czepiel et al. (1996): “The soils at each location were sampled at 5-c m intervals from the surface to a depth of 25cm...The distribution of oxidation in the soil column was similar in each profile with maximum occurring in the 5 to 10-cm depth interval in seven of the nine profiles (Figure 1) .”

• Soil samples were taken from the surface (25-cm) of the land fill; however it is important to note that
the entire landfill was covered by 1-2 m of sandy-clay loam cover material (pg. 16721). Czepiel et al.
(1996) also conclude that “the modeled estimate of annual whole landfill oxidation of 10% is consistent
with the current low range of oxidation estimate,” however, “...a climate factor should therefore enter
into any future estimates of landfill CH 4 

## emissions in which cover soil oxidation is considered.” ( pg. 16728).

De Visscher et al. (1999): “By combining this kinetic data with t he soil gas composition data, the actively methane oxidizing zone in the soil column could be determined and an in si tu assessment of oxygen limitation could be performed. Methane oxidation takes place mainly in the top 30 c m of covering soil.”

• Prior to the above quotation, De Visscher et al. state t hat “concentration profiles in a landfill cover soil
are hard to interpret. The gradients that develop are t he result of diffusion, reaction, and gas flow.
Furthermore, the gas flow rate depends on the depth of the col umn. This can be deduced from the
stoichiometry of the process...” (pg. 1856). De Visscher et al. specifically note a link between gas
flow rate and depth.

Hilger et al. (2000): “The CH 4 

## oxidation potential of soil from the laboratory soil columns is prese nted by horizon in Table 4...The average CH 4 

## oxidation potential measured from the top three horizon of all columns [0 to 15 cm] significantly exceeded that of the bottom three horizons [15 to 30 cm] (p<0.001), where O 2 

## was more limited (Table 1).”

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## 13 • The Hilger study does not contain any information regarding t he soil cover of the landfill from which
fresh core samples were taken (the Renaissance Park l andfill in Charlotte, NC), however the study does

indicate that the landfill is closed and has since been converted into recreational fields (pg. 458) .

Kightley et al. (1995): concluding that “our data show that soil microbial c ommunity adapts rapidly to the presence of elevated CH 4 

## concentrations and can effectively reduce emissions of CH 4 

## from the surface of landfill soil. The capacity for CH 4 

## oxidation in soil is related to the depth of O 2 

## penetration and to the nutrient status of the soil, which may regulate the extent to which the met hanotrophic community can develop.”

• See the discussion for Kightley et al. (1995) in Section 5.2.1 of this memorandum.

• With respect to this section and in response to pages 17- 18 of the petition stating that “many of the
studies conclude that methane oxidation primarily occurs in the upper part of the cover, close to the
surface, and several of the studies do not even calculate methane oxidation below a depth of 30 to 45
cm (15 to 18 inches).”

o The soil samples were collected from the top 15-cm of vari ous landfills (minus any turf) and
were then sieved and packed to a depth of 90-cm.

o Figure 8 in this article shows rates of methane oxidation potential for the 4 subsamples of
coarse sand (1 control and 3 amended with different nutri ent sources). The control and the 2
subsamples amended with K2HPO4 and sewage sludge did show a peak in methane oxidation
potential at a depth of approximately 20-cm. Rates of meth ane oxidation potential were greater
than zero at depths below 20-cm, although significantly less than that observed at 20-cm.

Scheutz and Kjeldsen (2003): “Vertical soil gas profiles showed that both methane and oxygen were often present between 20- and 40-cm depths. From 60-cm depth, the soil gas consist ed of almost pure LFG—with only very low or no oxygen present.”

• The authors note that “in landfill top covers, methane and oxygen counter-gradients may appear due to
emission of methane from the waste and diffusion of oxygen from a mbient air. Landfill soil covers thus often appear with an upper aerobic zone of 20-50cm and a lower an aerobic zone of 20-50cm in a 1m
top cover, providing living conditions for different bacteria,” (pg. 5143) and state that their study

consisted of soil retrieved down to 90-cm below the surface of the landfill (pg. 5144). The authors
additionally note the complexity of methane oxidation and physical gas transport within a column of
soil (pg. 5146).

Wilshusen et al. (2004): showing the change in CH 4 

## concentration at various depths and demonstrating that gas concentration typically begins to decline (indicating methane oxidation is taking place) at a depth of 40cm).

• Wilshusen et al. performed experiments on columns composed solely of compost compromised of
municipal leaf compost co-composted with manure from a loc al zoo (pg. 644) which does not represent
a typical landfill.

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## 14 5.2.3 “This is consistent with Lancaster’s actual oxidati on value, which was conservatively determined to be an average of greater than 34%, wi th a low methane flux rate ranging from 0.90g CH4/m2/d to 3.96g CH4/m2/d. However, as an active landfill, it is primarily

under intermediate cover of less than 24 inches and thus, under the Final Rule, would
have to use the default oxidation fraction of 10%.” Pg. 23 paragraph 2

Chanton et al. (2011): Table 2, 316

• This Chanton study provided a wide range of soil covers during exp erimentation; “generally the covers
investigated at these landfills were intermediate covers composed of a single 30-122-cm thick layer of
native soils, most commonly clay. One daily cover was inves tigated” (pg. 313).

• Chanton et al. state that “mean values for CH 4 

## oxidation efficiency calculated from chamber-derived

CH 4 

## varied from 34-41% across the different landfills (pg. 316) and additionally state that their results

are consistent with a recent literature review which reported a mean value of 35 ± 6% for the fraction of

CH 4 

## oxidized. It is important to note that the recent lit erature review mentioned is also another
Chanton study. The study notes that “[their] data...indicate that landfill CH 4 

## oxidation is, at a
minimum, 25% for landfills with gas collection systems” ( pg. 317). From the expansive range of cover
depth indicated by Chanton et al., the reader is unable to de termine if the 34-41% oxidation resulting
from the study is indicative of plots evenly represented throu ghout this range (30-122cm) or weighted

to one extreme.

Goldsmith et al. (2012): Table 2 (Location C5), 192



# • The location WM cited in the petition is only one of multip le studies reviewed by Goldsmith et al.
(2012). The location also has the second lowest flux measurem ents of all sites studied (pg. 192).
Goldsmith et al. studied a large variety of landfill cove rs: open face, daily cover, temporary cover,
intermediate cover and final cover. “Significant measure ments were conducted on intermediate soil
covers due to ease of availability and the fact that the y often constitute the majority of the landfill
cover” (pg. 194). The authors state that the oxidation capa city of the soil used in landfill covers has
been found to be greater than 10% (pg. 185) and note in their conclusion that “the western
Mediterranean landfills, for example, generally used just 30-45-cm of sandy clay soil for intermediate
cover, as compared to 60-cm loam to clay soils for most of the humid continental sites. Final soil
covers ranged from 1-2-m in soil thickness at all landfills” (pg. 194).



# 6. Conclusions

• 27 peer-reviewed studies were reviewed previously to promulgate a soil depth requirement of 24 inches
in Table HH-4 to Subpart HH of Part 98. These studies were i ncluded in either or both the SWICS
2012 Addendum or in RTI 2011 (a literature review of landfill m ethane oxidation studies). A total of
61 data points where both the fraction of methane oxidized an d soil cover depth are presented across
these studies, including49 field measurements and 12 column measur ements. Table A-1 summarizes
key data from the peer-reviewed literature across all 27 studies (also presented in SWICS, 2012).

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## 15 • 85% (or 52 of 61) of the data points gathered from these studie s where both the methane oxidized and
cover depth were reported had a cover depth of 24 inches or above . All of the experiments in these

studies were conducted, or can be assumed, to have been c onducted at a landfill or landfill-type
environment (for column studies) with a cover.

• 15 of the 27 peer-reviewed studies were referenced by the p etitioner to aid in their arguments against
EPA’s cover requirements in Table HH-4. The portions of t hese studies used by the petitioner are

elaborated on in Section 5.2 of this memorandum. Of these 15 studies, 14 were conducted at landfill
environments and 13 (or 93%) of these included an average cover de pth of 24 inches or greater (in the
original peer-reviewed journal article or in SWICS 2012).

• None of the 27 peer-reviewed studies specifically investigated the optimal cover depth for methane
oxidation. A conclusion cannot be made that cover depth does not i mpact methane oxidation because a
cover material of various depths was included in all measu rements. However, several studies measured
methane and/or oxygen profiles in the surface cover soil and these measurements indicate that the
majority of oxidation occurs in the top 12 to 15 inches of the cover soil.

• In areas near passive vent pipes, a significant portion of the methane emissions is expected to be
released via the vent pipe (as suggested by low methane flux in soil areas near passive vent pipes as
noted by Liptay et al., 1998 and Chanton and Liptay, 2000), and therefore bypass the surface soil. The
oxidation factor for the methane released via the passive vent is expected to be 0, so it may be
appropriate to limit the use of high oxidation fractions for landfills with passive vents. It is important to
note that the Intergovernmental Panel on Climate Change 2006 Guide lines (IPCC, 2006) recommends
the use of oxidation fractions ranging from 0 to 10 percent la rgely due to the fact that landfill gas will
flow primarily through channels of least flow resistance, which one would expect the passive vents to
be. If there are fissures in the soil cover (or passive vent systems), a significant portion of the landfill
gas will be released without any oxidation occurring. Mor e explicitly than the IPCC (IPCC, 2006), the
EPA Climate Leaders (EPA Climate Leaders, 2004) note that “passive controls may reduce the
potential for methane to be oxidized.”



# References

Barlaz et al. 2004. Evaluation of a biologically active cover f or mitigation of landfill gas emissions. Environmental Science and Technology, 38: 4891-4899.

Bogner et al. 1997. Kinetics of Methane Oxidation in a Landfill Cover Soil: Temporal Variations, a WholeLandfill Oxidation Experiment, and Modeling of Net CH4 Emis sions. Environmental Science and Technology, 31: 2504-2514.

Cabral et al. 2010. Quantifying microbial methane oxidati on efficiencies in two experimental landfill biocovers using stable isotopes. Water Air and Soil Pollution, 209(1): 157-172.

Chanton et al. 2008. Improved field methods to quantify meth ane oxidation in landfill cover materials using stable carbon isotopes. Environmental Science and Technology, 42: 665-670.

Chanton et al. 2011. Landfill Methane Oxidation Across Cli mate Types in the U.S. Environmental Science and Technology, 45: 313-319.

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## 16 Chanton J. and Liptay K. 2000. Seasonal variation in metha ne oxidation in landfill cover soils as determined by an in situ stable isotope technique. Global Biogeochemical C ycles, 14: 51-60.

Christopherson et al. 2001. Lateral Gas Transport in Soil adjacent to an Old Landfill: Factors Governing Emissions and Methane Oxidation. Waste Management and R esearch, 19: 595-612.

Czepiel et al. 1996. Quantifying the effect of oxidation on l andfill methane emissions. Journal of Geophysical Research, 101(D11): 16721-16729.

De Visscher et al. 1999. Methane Oxidation in Simulated La ndfill Cover Soil Environments. Environmental Science and Technology, 33: 1854-1859.

Gebert et al. 2011a. Can soil gas profiles be used to ass ess microbial CH 4 

## oxidation in landfill covers? Waste Management, 31: 987-994.

Gebert et al. 2011b. Relevance of soil physical properties f or the microbial oxidation of methane in landfill covers. Soil Biology and Biochemistry, 43: 1759-1767.

Goldsmith et al. 2012. Methane emissions from 20 landfills acro ss the United States using vertical radial plume mapping. Journal of the Air & Waste Management Association , 62: 183-197.

Hilger et al. 2000. Methane oxidation and microbial exopo lymer production in landfill cover soil. Soil Biology and Biochemistry, 32: 457-467.

Huber-Humer et al. 2009. Approaches to assess biocover performa nce on landfills. Waste Management, 29:

2092-2104.

EPA Climate Leaders. 2004. Direct Emissions from Municipal So lid Waste Landfilling, Section 2: Methods for Estimating CH 4 

## Emissions. Available at http://www.epa.gov/climateleadership/documents/resources/pr otocol-solid_waste_landfill.pdf

. IPCC (Inter-Governmental Panel on Climate Change). 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Volume 5: Waste, Chapter 3: Solid Wast e Disposal. Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miw a K., Ngara T. and Tanabe K. (eds). Published: IGES, Japan.

Kightley et al. 1995. Capacity for methane oxidation in lan dfill cover soils measured in laboratory-scale microcosms. Applied and Environmental Microbiology, 61: 592-610.

Liptay et al. 1998. Use of stable isotopes to determine met hane oxidation in landfill cover soils. Journal of Geophysical Research, 103: 8243-8250.

Rachor et al. 2011. Assessment of the methane oxidation c apacity of compacted soils intended for use as landfill cover materials. Waste Management, 31: 833-842.

RTI 2011. Updated Research on Methane Oxidation in Landfil ls. Memorandum prepared by K. Weitz (RTI) for R. Schmeltz (EPA, January 14, 2011.

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. Environmental Science and Technology,

37: 5143-5149.

Scheutz et al. 2009. Microbial methane oxidation processes a nd technologies for mitigation of landfill gas emissions. Waste Management and Research, 27: 409-455.

Schroth et al. 2012. Above- and below-ground methane fluxes an d methanotrophic activity in a landfill-cover soil. Waste Management, 32: 879-889.

Spokas, K.A. and Bogner, J.E. 2011. Limits and dynamics of met hane oxidation in landfill cover soils. Waste Management, 31(5): 823-832.

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## 17 Solid Waste Industry for Climate Solutions (SWICS) Metha ne Oxidation Addendum 2012, dated November 19, 2012

Stern et al. 2007. Use of a biologically active cover to red uce landfill methane emissions and enhance methane oxidation. Waste Management, 27: 1248-1258.

Wilshusen et al. 2004. Long-term behavior of passively aerate d compost methanotrophic biofilter columns. Waste Management, 24: 643-653.

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## 18 

# AppendixReview of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International19Table A-1. Summary of Oxidation Study Data: Cover Material,Study Type, and Cover Depth for Studies Included in SWICS2012

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceOtherMaterialSandy loamlandfill coverField Isotopefractionation0.456+ 0.2158+0.25 0.028 No No gas collection system, butmeasurements were taken atintermediate cover (one 45cm sandy clay with wellvegetated topsoil, and the2nd at 15 cm non-vegetated)17.72 No explicitmention, buthadintermediatecoverSept to Febin FLAbichou et al.,2006Clay Sandy claylandfill coverField Isotopefractionation(field isotopechambercollected)0.564+ 0.3420+0.14 0.039 No No gas collection system, butmeasurements were taken atintermediate cover (one 45cm sandy clay with wellvegetated topsoil, and the2nd at 15 cm non-vegetated)5.91 No explicitmention, buthadintermediatecoverFeb to May inFLAbichou et al.,2006Sand Sandy soil Column Repackedcolumn withCH4 advectionNR NR 0.77 NR NA NR Ahn et al.,2002Organic Compostlandfill coverField Isotopefractionation(field isotopechambercollected)0.041+ 0.0331+0.54 0.136 Yes Biocover; 0.15 m thick claylayer over the waste, followedby 0.15 m of tire chips, then 1m of yard waste compost51.18 No explicitmentionApril, June,Sep in KYBarlaz et al.,2004Clay Clay landfillcoverField Isotopefractionation(field isotopechambercollected)1.216+ 0.8963+0.21 0.056 Yes soil cover, clay 39.37 No explicitmentionApr, Jun, Sepin KYBarlaz et al.,2004OtherMaterialEuropeanlandfill coversField Isotopefractionation0.4239+1.5460+0.84 0.023+Yes 39.37 5.8 to 26.9 Bergamaschiet al., 1998Clay Silty claylandfill coverColumn Undisturbedcolumn with 135to 145 ppmvCH4 diffusion0.004+ 0.0005+NR NR NA 49.21 Closed (fiNAlcover 1980s)Jun, Sep,Nov in ILBogner et al.,1997Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International20

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceClay Silty claylandfill coverColumn Undisturbedcolumn with 1 to8 % CH4diffusion1.156+ 0.2927+NR NR NA 49.21 Closed (fiNAlcover 1980s)Jun, Sep,Nov in ILBogner et al.,1997Sand Sand Scholl,CAField Soil gas probeisotope methodNR NR 0.48 0.016 Yes Final cover 30-244 cm 53.94 Closed(assumed fromfiNAl cover)Annual cycle Bogner et al.,2011Sand Sand Marina,CAField Field isotopechambercollectedNR NR 0.30 0.020 Yes 30-120 cm (fraction oxidizednot presented by landfill insource); avg cover depthpresented here; cover depthsranged from daily,intermediate, to final cover at2 sites29.53Open (assumedfromintermediatecover)Annual cycle Bogner et al.,2011Sand Sand Scholl,CAField Field isotopechambercollectedNR NR 0.52 0.180 Yes 30-275 cm (fraction oxidizednot presented by landfill insource); avg cover depthpresented here; cover depthsranged from daily,intermediate, to final cover at2 sites29.53 Open(assumedfromintermediatecover)Annual cycle Bogner et al.,2011Sand Sand Marina,CAField Soil gas probeisotope methodNR NR 0.40 0.032 Yes Intermediate cover 10-50 cm 11.81Open (assumedfromintermediatecover)Annual cycle Bogner et al.,2011Sand Sand landfillcoverField Isotopefractionation(field isotopechambercollected)0.172+ 0.2771+0.42 0.095+No Reported as 0.3 to 0.8;average presented here21.65 0.4 to 24.8 Borjesson etal., 2001OtherMaterialSandy loamlandfill coverField Isotopefractionation3.795+ 2.6892+0.26 0.048+Yes See Table FootnoteaSee coverdepthcomments-0.3 to 26.8 Borjesson etal., 2007Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International21

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceOrganic Wood chipsand sludgeField Plume tracerand isotopefractionation(isotopicanalysis ofwhole landfillplume)NR NR 0.16 0.031 Yes See Table FootnoteaSee coverdepthcomments7 Borjesson etal., 2007Organic Wood chipsand sludgeField Plume tracerand isotopefractionation(isotopicanalysis ofwhole landfillplume)NR NR 0.25 0.003 Yes See Table FootnoteaSee coverdepthcomments17 Borjesson etal., 2007OtherMaterialSewagesludge andmineral soilsField Plume tracerand isotopefractionationNR NR 0.07 0.023 Yes See Table FootnoteaSee coverdepthcomments6 Borjesson etal., 2007OtherMaterialSewagesludge andmineral soilsField Plume tracerand isotopefractionationNR NR 0.015 0.011 Yes See Table FootnoteaSee coverdepthcomments-2 Borjesson etal., 2007OtherMaterialMineral soil Field Plume tracerand isotopefractionationNR NR 0.40 0.026 Yes See Table FootnoteaSee coverdepthcomments9 Borjesson etal., 2007OtherMaterialMineral soil Field Plume tracerand isotopefractionationNR NR 0.38 0.032 Yes See Table FootnoteaSee coverdepthcomments5 Borjesson etal., 2007OtherMaterialMulch andtopsoil landfillcoverField Isotopefractionation1.678+ 0.2114+0.26 0.040 No 42.91 Closed 8 to 35 Chanton andLiptay, 2000Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International22

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceClay Clay landfillcoverField Isotopefractionation(field isotopechambercollected)13.517+1.8114+0.14 0.02 No 39.37 Closed 6 to 32 Chanton andLiptay, 2000Organic Compost Field Isotopefractionation(field isotopechambercollected)NR NR 0.29 0.065 No 43.31 No explicitmentionall year, FL Chanton et al.,2008OtherMaterialLoamy landfillcoverField IsotopefractionationNR NR 0.12 0.025+No 42.13 No explicitmentionall year, FL Chanton et al.,2008Organic Mulch Field Isotopefractionation(isotopechambercollected)NR NR 0.40 0.033 No 39.37 No explicitmentionall year, FL Chanton et al.,2008Organic Mulch Field Isotopefractionation(field isotopechambercollected)NR NR -0.01 0.045 No 27.56 No explicitmentionall year, FL Chanton et al.,2008Clay Clay landfillcoverField Isotopefractionation(field isotopechambercollected)NR NR 0.08 0.030 No 7.87 No explicitmentionall year, FL Chanton et al.,2008Sand Sand, KirbyCanyon CAField Field isotopesurface air0.024 0.0100 0.56 0.24 Yes 0.3 - 1.22 mb29.92 No explicitmentionJan 2008 CAChanton et al.,2011Clay Clay,Altamount CAField Field isotopesurface air0.056 0.0120 0.27 0.08 Yes 0.3 - 1.22 mb29.92 No explicitmentionOct 2009 CAChanton et al.,2011Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International23

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceSand Sand, KirbyCanyon CAField Field isotopesurface air0.078 0.0000 0.69 0.07 Yes 0.3 - 1.22 mb29.92 No explicitmentionJune 2008CAChanton et al.,2011OtherMaterialSandy clayDADS COField Field isotopesurface air0.204 0.1370 0.64 0.12 Yes 0.3 - 1.22 mb29.92 No explicitmentionOct 2007 COChanton et al.,2011Clay Clay,Clearview MSField Field isotopesurface air0.365 0.1480 0.15 0.09 Yes 0.3 - 1.22 mb29.92 No explicitmentionNov 2009 MSChanton et al.,2011Clay Clay, TricitiesCAField Field isotopesurface air0.505 0.1480 0.24 0.12 Yes 0.3 - 1.22 mb29.92 No explicitmentionFeb 2008 CAChanton et al.,2011Clay Clay, OL 7 KYField Field isotopesurface air0.688 0.2390 0.28 0.12 Yes 0.3 - 1.22 mb29.92 No explicitmentionDec 2007 KYChanton et al.,2011OtherMaterialSilty clay loamSuburban OHField Field isotopesurface air0.712 0.2690 0.06 0.02 Yes 0.3 - 1.22 mb29.92 No explicitmentionDec 2009 OHChanton et al.,2011Clay Clay,Clearview MSField Field isotopesurface air1.079 0.1470 0.14 0.08 Yes 0.3 - 1.22 mb29.92 No explicitmentionApr 2009 MSChanton et al.,2011Clay Clay, PineRidge MSField Field isotopesurface air1.233 0.3830 0.11 0.05 Yes 0.3 - 1.22 mb29.92 No explicitmentionApr 2009 MSChanton et al.,2011Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International24

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceClay Clay, TricitiesCAField Field isotopesurface air1.349 0.0000 0.33 0.04 Yes 0.3 - 1.22 mb29.92 No explicitmentionAug 2008 CAChanton et al.,2011Clay Clay,MaplewoodVAField Field isotopesurface air1.927 0.1500 0.31 0.16 Yes 0.3 - 1.22 mb29.92 No explicitmentionApr 2008 VA Chanton et al.,2011Clay Clay, OL 7 KYField Field isotopesurface air1.982 0.0000 0.29 0.07 Yes 0.3 - 1.22 mb29.92 No explicitmentionJan 2008 KYChanton et al.,2011Clay Clay, PineRidge MSField Field isotopesurface air2.295 0.5300 0.22 0.01 Yes 0.3 - 1.22 mb29.92 No explicitmentionDec 2009 MSChanton et al.,2011Clay Clay,Redwood CAField Field isotopesurface air2.431 1.8200 0.51 0.23 Yes 0.3 - 1.22 mb29.92 No explicitmentionJun 2009 CAChanton et al.,2011OtherMaterialSilty clay loam+ compostedyard wasteOL8 KYField Field isotopesurface air3.540 1.2200 0.59 0.23 Yes 0.3 - 1.22 mb29.92 No explicitmentionJuly 2007 KYChanton et al.,2011Clay Clay, NewSpruce MNField Field isotopesurface air4.112 0.0000 0.95 0.03 Yes 0.3 - 1.22 mb29.92 No explicitmentionAug 2007 MNChanton et al.,2011Clay Clay,Springhill FLField Field isotopesurface air6.274 1.8000 0.20 0.08 Yes 0.3 - 1.22 mb29.92 No explicitmentionApr 2007 FL Chanton et al.,2011Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International25

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceClay Clay, OL 7 KYField Field isotopesurface air6.512 0.0000 0.53 0.12 Yes 0.3 - 1.22 mb29.92 No explicitmentionJuly 2007 KYChanton et al.,2011Clay Clay, OL 5 KYField Field isotopesurface air7.47 0.0000 0.43 0.06 Yes 0.3 - 1.22 mb29.92 No explicitmentionAug 2007 KYChanton et al.,2011Clay Clay, MetroWIField Field isotopesurface air7.7220 2.8950 0.16 0.09 Yes 0.3 - 1.22 mb29.92 No explicitmentionMay 2008 WIChanton et al.,2011OtherMaterialSandy loamAtlantic VAField Field isotopesurface air8.329 0.0000 0.34 0.04 Yes 0.3 - 1.22 mb29.92 No explicitmentionAug 2008 VAChanton et al.,2011Clay Clay, SpruceMNField Field isotopesurface air10.079 0.0000 0.47 0.03 Yes 0.3 - 1.22 mb29.92 No explicitmentionJul 2008 MN Chanton et al.,2011Clay Clay, OL 7 KYField Field isotopesurface air10.760 5.3000 0.31 0.15 Yes 0.3 - 1.22 mb29.92 No explicitmentionMar 2007 KYChanton et al.,2011OtherMaterialSilty clay loamSuburban OHField Field isotopesurface air11.050 0.0000 0.25 0.04 Yes 0.3 - 1.22 mb29.92 No explicitmentionSept 2009OHChanton et al.,2011Clay Clay,Springhill FLField Field isotopesurface air11.100 0.7220 0.29 0.16 Yes 0.3 - 1.22 mb29.92 No explicitmentionMay 2006 FLChanton et al.,2011Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International26

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceOtherMaterialSilty clay loamCentral IAField Field isotopesurface air12.340 0.0000 0.82 0.06 Yes 0.3 - 1.22 mb29.92 No explicitmentionAug 2007 IA Chanton et al.,2011Clay Clay,Atascocita TXField Field isotopesurface air15.318 4.2800 0.13 0.08 Yes 0.3 - 1.22 mb29.92 No explicitmentionNov 2008 TXChanton et al.,2011Clay Clay, OL 5 KYField Field isotopesurface air15.627 3.8900 0.41 0.16 Yes 0.3 - 1.22 mb29.92 No explicitmentionJuly 2007 KYChanton et al.,2011Clay Clay,MaplewoodVAField Field isotopesurface air16.700 0.0000 0.41 0.05 Yes 0.3 - 1.22 mb29.92 No explicitmentionSept 2008 VAChanton et al.,2011Clay Clay,Atascocita TXField Field isotopesurface air16.736 7.9200 0.30 0.15 Yes 0.3 - 1.22 mb29.92 No explicitmentionFeb 2008 TXChanton et al.,2011Clay Clay, OL 7 KYField Field isotopesurface air22.820 0.0000 0.20 0.04 Yes 0.3 - 1.22 mb29.92 No explicitmentionJuly 2006 KYChanton et al.,2011Clay Clay, MetroWIField Field isotopesurface air22.920 8.6000 0.31 0.12 Yes 0.3 - 1.22 mb29.92 No explicitmentionOct 2008 WI Chanton et al.,2011OtherMaterialSilty clay loam+ compostedyard wasteOL8 KYField Field isotopesurface air29.750 0.0000 0.70 0.04 Yes 0.3 - 1.22 mb29.92 No explicitmentionJuly 2006 KYChanton et al.,2011Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International27

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceClay Clay, OldSpruce MNField Field isotopesurface air30.729 8.0800 0.33 0.07 Yes 0.3 - 1.22 mb29.92 No explicitmentionAug 2009 MNChanton et al.,2011SandSand adjacentto landfillField Isotopefractionation(field isotopechambercollected)0.149+ 0.1372+0.28 0.152 NR Reported as "na" in SWICS201239.37 Closed 2 to 25 Christophersenet al., 2001SandSand adjacentto landfillField CH4 and CO2mass balance1.097+ 0.4969+0.89 NR NR Reported as "na" in SWICS201239.37 Closed 2 to 25 Christophersenet al., 2001OtherMaterialSandy-clayloam landfillcoverColumn Incubation andmodel (enclosedsample withCH4 diffusion)1.830+ 0.2642+0.1 NR No Reported as 1 to 2 m;average presented here59.06 No explicitmention19 Czepial et al.,1996OtherMaterialSandy-clayloam landfillcoverField Chambers andestimatedfraction oxidized0.906+ 0.2506+NR NR No Reported as 1 to 2 m;average presented here59.06Sept to Oct inNHCzepial et al.,1996bOtherMaterialSandy-clayloam landfillcoverField Plume tracerand estimatedfraction oxidized1.031+ 0.0586+NR NR No Reported as 1 to 2 m;average presented here59.06 No explicitmentionSept to Oct inNHCzepial et al.,1996bOtherMaterialSandy loamlandfill coverColumn Repackedcolumn withCH4 advection15.00000.2725+0.65 0.020+NA 23.62 Closed and/orAbandoned18 to 26 De Visscher etal., 1999OtherMaterialLoamyagriculturalsoilColumn Repackedcolumn withCH4 advection8.236+ 0.2725+0.61+ 0.020+NA 23.62 Closed and/orAbandoned18 to 26 De Visscher etal., 1999Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International28

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceOtherMaterialSandy loamlandfill coverColumn Repackedcolumn withCH4 advection3.535 0.0757 0.21 0.005 NA Cores were collected bydriving a 30 cm long by 5 cmwide pipe into the landfillcover surface . . . About 20cm of soil was recovered fromeach core.12.20 Closed 22 Hilger et al.,2000Organic Compost Column Repackedcolumn withCH4 advection9.423+ NA 1 NA NA 23.62 18 Humer andLechner,1999OtherMaterialLoam Column Repackedcolumn withCH4 advectionNR NR 0.42 NR NA NR Humer andLechner, 2001Clay Clay landfillcoverColumn Repackedcolumn withCH4 advection6.800 0.3000 0.40 0.018 NA 35.43 No explicitmention19 Kightley et al.,1995Sand Fine sandlandfill coverColumn Repackedcolumn withCH4 advection6.9 0.3 0.41 0.018 NA 35.43 No explicitmention19 Kightley et al.,1995Sand Coarse sandlandfill coverColumn Repackedcolumn withCH4 advection10.4 0.1 0.61 0.006 NA 35.43 No explicitmention19 Kightley et al.,1995OtherMaterialLandfill "A"coverField IsotopefractionationNR NR 0.28 0.108 NR No explicitmention21 to 30 Liptay et al.,1998OtherMaterialLandfill "B"coverField IsotopefractionationNR NR 0.19 0.014 NR No explicitmention20 to 28 Liptay et al.,1998Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International29

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceOtherMaterialSandy-clayloam landfillcoverField IsotopefractionationNR NR 0.68 0.093 NR No explicitmention22 to 29 Liptay et al.,1998OtherMaterialRochesterlandfill coverField IsotopefractionationNR NR -0.03(reportedas 0.00inSWICS2012)0.035 NR No explicitmentionAug in NH Liptay et al.,1998OtherMaterialSpringfieldlandfill coverField IsotopefractionationNR NR 0.01 0.042 NR No explicitmention14 to 18 Liptay et al.,1998OtherMaterialWaylandlandfill coverField IsotopefractionationNR NR 0.32 0.053 NR No explicitmention18 to 23 Liptay et al.,1998SandSand fractions0.24 to 4 mmColumn nr NR NR 0.52 NR NA NR Pawlowsda etal., 2003; citedby Rachor etal., 2002Sand Loamy sandlandfill coverColumn Repackedcolumn withCH4 advectionof 65 mol m^-2d^-123.725 1.7299 0.37 0.027 NA NR No explicitmention22 Scheutz andKjeldsen, 2003Sand Loamy sandlandfill coverColumn Repackedcolumn withCH4 advectionof 4.8 mol m^-2d^-14.608+ 0.0842+0.96+ 0.017+NA No explicitmention22 Scheutz andKjeldsen, 2003OtherMaterialLoam Column Repackedcolumn withCH4 advectionNR NR 0.81 NR NA Uncontrolled landfill with noliners or gas extractionsystem. Depth ranged from5-90 cm, with measurementstaken every 5 cm18.70 Open(assumed)NR Scheutz et al.,2003Review of Oxidation Studies and Associated Cover Depth in thePeer-Reviewed LiteratureJune 2015RTI International30

Cover Material Cover Material Detailed Study Type Method Oxidation Rate (mol m

- 2 d1 ) Std. Error Oxidation Rate Fraction Oxidized Std. Error Fraction Ox Gas Collection Cover Depth Comments Cover Depth (inches) LF was Open or Closed Soil Temp. ( °C , or month and state) ReferenceOrganic Yard-wastecompostField Isotopefractionation(field isotopechambercollected)0.108 0.0338 0.38 0.031 No See Footnotec19.69 Closed all year, FL Stern et al.,2007OtherMaterialFine sandyloam landfillcoverField Isotopefractionation0.141 0.0281 0.19 0.027 No See Footnotec13.78 Closed all year, FL Stern et al.,2007Sand Sandy soil Column Repackedcolumn withCH4 advection4.366+ 0.2634+0.44+ 0.033+NA 47.24 30 to 40Visvanathan etal., 1999OtherMaterialSand withclay landfillcoverColumn Undisturbedcolumn withCH4 diffusion3.813 0.2914 NR NR NA 3.94 25 Whalen et al.,1990Organic Compost Column Repackedcolumn withCH4 advection6.250 0.6250+0.19 0.019+NA Compost study; not landfillenvironment19.69 Not a landfill;compost22 Wilshusen etal., 2004a6 Swedish landfills (2 closed, 4 open) investigated; fraction oxidized varied with cover type; the info presented here is as summarized in SWICS 2012. Page 2 states cover depthwas 0-30 cm (Cover Soils: Common Characteristics)bnot presented by landfill in source; average coverdepth presentedcExperiment was set up over waste that had been covered for 8 yrs by 20-60 cm of sandy clay overlain by 20-50 cm of fine sandy loam; 10-cm thick layers of glass cullet were placedover the entire test cells, followed by a 50-cm thick mulch layer in 1 area.OX = oxidation rateNR = not reportedNA = not applicable