Summary of Expert Review Comments and Responses: Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016 Chapter 3. Energy


<&EPA

United States
Environmental Protection
Agency

Summary of Expert Review Comments and Responses:

Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016

April 2018
U.S. Environmental Protection Agency
Office of Atmospheric Programs
Washington, D.C.

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Responses to Comments Received during the Expert Review Period on
the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016

Preface	3

Chapter 3. Energy	4

3.1 CH4 and N20 from Mobile Combustion - Methodological Updates in Response to Changes to
FHWA's Gasoline Consumption Estimation Models	4

3.1 CH4 and N20 from Mobile Combustion - Updated Methodology for Estimating CH4 and N20
Emissions from Alternative Fuel Vehicles	4

3.1 CH4 and N20 from Mobile Combustion - Updated Non-Highway CH4 and N20 Emission Factors	6

3.1 CH4 and N20 from Mobile Combustion - Updated On-Highway CH4 and N20 Emission Factors	7

Chapter 4. Industrial Processes and Product Use (IPPU)	7

4.17 Iron and Steel Production and Metallurgical Coke Production	7

Chapter 6. Land Use, Land Use Change and Forestry (LULUCF)	9

6.1	Representation of the US Land Base	9

6.2	Forest Land Remaining Forest Land	10

6.8 Wetlands Remaining Wetlands	10

6.10 Settlements Remaining Settlements	11

6.10 Settlements Remaining Settlements - Changes in Yard Trimmings and Food Scrap Carbon Stocks
in Landfills	11

Chapter 7. Waste	13

7.1	Landfills	13

7.2	Wastewater Treatment	25

Annex 3: Methodological Descriptions for Additional Source or Sink Categories	27

Annex 3.14 Methodology for Estimating CH4 Emissions from Landfills	27

Appendix A: List of Reviewers and Commenters	28

Appendix B: Dates of review	29

Appendix C: EPA Charge Questions to Expert Reviewers	30

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Preface

EPA thanks all commenters for their interest and feedback on the annual Inventory of U.S. Greenhouse
Gas Emissions and Sinks. In an effort to continue to improve the estimates in the annual Inventory of
U.S. Greenhouse Gas Emissions and Sinks, EPA distributed draft chapters of the Inventory of U.S.
Greenhouse Gas Emissions and Sinks: 1990-2016 for a preliminary Expert Review of estimates and
methodological updates prior to release for Public Review. The Expert Review ranged from 15 to 30 days
by sector, and included charge questions to focus review on methodological refinements and other
areas identified by EPA as needing a more in-depth review by experts. The goal of the expert review is to
provide an objective review of the Inventory in order to ensure that the final Inventory estimates and
document reflect sound technical information and analysis.

EPA received 61 unique comments as part of the expert review process. The verbatim text of each
comment extracted from the original comment letters is included in this document, arranged by sectoral
chapters. No comments were received on the Draft Agriculture Chapter. EPA's responses to comments
are provided immediately following each comment excerpt. The list of reviewers, dates of review and all
charge questions distributed to reviewers are included in the Annex to this document.

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Chapter 3.Energy

3.1 CH4 and N20 from Mobile Combustion - Methodological Updates
in Response to Changes to FHWA's Gasoline Consumption Estimation
Models

Comment: Decision to Update Data is Clear

Generally, the proposal to update the historical (1990-2015) motor gasoline time series data by
incorporating estimates of historic lawn and garden and recreational vehicle fuel use from the EPA's
NONROAD model is relatively clear and transparent. Given that the last "major" update of the
NONROAD model occurred in 2008, it is likely that the version that was embedded into MOVES for the
release of MOVES2014a is very outdated. Therefore, EPA should devote an effort to ensuring that: (a) its
estimates using the NONROAD version of the model that is embedded in MOVES are based on updated
estimates of equipment populations, activity, fuel efficiency and emission factors, and (b) the latter are
consistent with the data, methodology and assumptions used by FHWA for its estimates of non-highway
gasoline usage.

Response: Although the NONROAD model was incorporated into the MOVES platform in 2014,
much of NONROAD's underlying equipment population and activity data are 15-20 years old. EPA
is currently developing updated non-road population and activity databases (as well as emission
rates), which will be available in future versions of MOVES.

3.1 CH4 and N20 from Mobile Combustion - Updated Methodology for
Estimating CH4 and N2O Emissions from Alternative Fuel Vehicles

Comment: Reporting Use of RNG in On-Road Vehicles

Based on our review by expert colleagues at Natural Gas Vehicles for America ("NGVAmerica"), which
includes many AGA member companies, AGA requests that EPA ensure that the Inventory accounts for
the use of Renewable Natural Gas ("RNG") in on-road natural gas vehicles. It is not clear to us whether
this has been done, and if so, where this data will be reflected in the Inventory. As the recent September
2017 EPA-AGA Renewable Natural Gas Workshop1 illustrated, there is increasing interest in using
purified biogas from landfills, waste water treatment plants and anaerobic digesters as a source of
renewable vehicle fuel. RNG used in natural gas vehicles now accounts for roughly 20 percent of the fuel
consumed in on-road NGVs, and the percentage is increasing every year. It is important for the Inventory
to report the growing use of RNG in on-road vehicles and the related reduction in GHG emissions from
vehicles.

1 See EPA Methane Challenge outreach and events web page at http://www.ttemidev.com/rng/workshop/
Response:

EPA will continue to research options for breaking out vehicles fueled with renewable natural gas.
Comment: Updated Data Available for GREET

This document proposed to rely on GREET 2016 for generating updated CH4 and N2O emission factor
estimates for alternative fuel vehicles. Argonne National Laboratory recently released GREET 2017
which is an updated version of GREET 2016. EPA should rely on the most current version of GREET
available.

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Response: Efforts to develop updated CH4 and N2O emission factors for AFVs precede the October
9, 2017 release of GREET 2017. EPA does, however, continue to endeavor to utilize the most up-to-
date data sources and calculation methodologies to produce this Inventory.

Comment: Numbering of Tables Inconsistent

The numbering of the tables in the text of the subsection labeled "CH4 and N2O Emissions by Vehicle and
Fuel Type" is not consistent with the table numbers shown in the titles of the tables displayed.

Response: EPA thanks commenter for feedback. Additional text has been added to the "CH4 and
N2O Emissions by Vehicle and Fuel Type" portion of the memo to more clearly indicate that the
"current" emission factors given in Table 6 are those which are described on Page 4 of the memo.
Additionally, the captions for Tables 7 and 8 have been modified to reflect that these tables display
"updated" emission factors, per the text description on Page 5.

Comment: Additional Text Needed for Clarity

In general, this document would benefit by additional text which more clearly explains the data and
assumptions which underlie each of the steps used to estimate CH4 and N2O emissions from alternative
fuel vehicles.

Response: EPA thanks commenter for feedback and will consider this for the current and future
reports.

Comment: Question about Reviewing EIA and GREET Estimates

Pg. 1, 2nd para: EPA states the following - "For VMT, energy use from EIA is divided by fuel economy
estimates from GREET to determine miles driven by fuel and vehicle class. Emission factors are
determined directly from GREET."

In performing the above calculation of VMT, EPA is implicitly assuming that EIA energy use values and
GREET fuel economy estimates are derived from identical populations of alternative vehicles
disaggregated by fuel and vehicle class. Has EPA checked the data and methodologies that underlie the
EIA and GREET estimates to verify that this assumption is correct? It may be appropriate to run some
sensitivity cases to determine the impact of this assumption on the final results.

Response: EPA thanks commenter for the suggestion to conduct additional analyses to determine
the extent to which energy use data from EIA and fuel economy values from GREET rely on
similar populations of AFVs. Such an analysis was not within the scope of this update.

Comment: Suggestion to Include Referenced Regression

Pg. 1, 2nd para, last sentence: It would be helpful to include a copy of the referenced regression analysis
and related regression equation statistics (e.g., R2 values) in an Appendix to this document.

Response: Regressions were performed, but details were not kept. The best fit was used in all cases.

Comment: Question about Data Comparison of Biodiesel Consumption

Did EPA compare the results of its regression analysis-based estimate of biodiesel consumption in 2000
with actual data?

Response: This comparison was not performed and was not within the scope of this update. EPA
will investigate data sources appropriate for conducting such a comparison, for possible inclusion
in future reports.

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Comment: Data Requested for EVs and PHEVs

Pg. 2, 1st para: EPA states the following assumption - "Fuel use per vehicle for EVs and PHEVs were
assumed the same as those for the public fleet vehicles surveyed and provided by EIA. This may
overestimate electricity usage as it is likely that fleet vehicles accumulate more annual mileage than
personal vehicles."

EPA should provide a range of values of the likely overestimate, especially for long range vehicles such
as Tesla S.

Response: While a comparison of accumulated mileage of fleet vs. personal EV and PHEV vehicles
would likely complement this memo, such an analysis is not within the scope of this work.

Comment: Further Elaboration on Table 2 Suggested

Pg. 2, Table 2: Table 2 is presented with virtually no explanation as to how the data which it contains are
being used in the analysis. How do EDTA data on annual sales of light-duty EV and PHEVs relate to the
EIA data tables on vehicle "counts?" It seems that sales data are being used interchangeably with vehicle
stock (i.e., vehicles in operation) data? Is this correct? If yes, then some additional explanatory text should
be incorporated into this document, for it is currently very vague and unclear with respect to
methodology.

Response: Cumulative PHEV and EV sales data are used to define vehicle counts. From 2011
onward, EPA assumes no vehicle scrappage. EIA data is used only to determine fuel/electricity use
per vehicle (it assumed that vehicle counts from EIA undercount EVs and PHEVs because only
fleet vehicles are included). EPA recognizes that future Inventories will need to account for vehicle
scrappage.

Comment: Question about Years in Table 1

Pg. 5, Table 1: What calendar year is being represented by the values shown in this table? i.e., what does
"current" mean in the context of calendar year representation? Such information would be useful in the
context of understanding the differences between the table on p. 5 and the tables shown on subsequent
pages.

Response: Clarification on Timing Language

"Current" in the context of Table 6 refers to emission factors that have been used to develop past
Inventories, through the 1990-2015 Inventory report. Should EPA adopt the emission factor
updates described in the memo, the "current" emission factors in Table 6 would then be
characterized as "previous."

3.1 CH4 and N2O from Mobile Combustion - Updated Non-Highway
CH4 and N2O Emission Factors

Comment: Proposal Written Clearly

Generally, the proposal to update the non-highway CH4 and N2O emission factors is written clearly,
comprehensively and transparently.

Response: EPA appreciates the feedback.

Comment: Question about Non-Highway Emission Factors

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What, if any, effort has EPA made to validate that the "new" non-highway CH4 and N2O emission factors
for each of the non-road equipment types mentioned in this update are indeed representative of actual,
real world operation? It would be useful to reference any such studies, research, etc., that support the
"new" estimates of emission factors that are shown in this paper.

Response: Due to a scarcity of in-use data of CH4 and N2O emissions from non-highway sources,
EPA has not attempted to validate the updated CH4 and N2O emission factors described in the
memo. Should in-use data become available in the future, EPA may attempt to validate the
emission rates described in this memo.

Comment: Suggestion to Add a Footnote to Tables

Given the significant changes in CH4 and N2O emissions that are shown for some categories in Tables
6,7,13 and 22 that are attributed to the change from "current" to "new" emission factors, it would be
useful to include a footnote to each of these tables that emphasizes the fact (if true) that no other changes
(i.e., to population and/or activity) were made that impact the comparisons.

Response: EPA agrees that the memo would benefit from table footnotes affirming that results
shown in the tables reflect only changes to emission factors and not from any changes to vehicle
population and activity inputs.

3.1 CH4 and N2O from Mobile Combustion - Updated On-Highway CH4
and N2O Emission Factors

Comment: Proposal Written Clearly

Generally, the proposal to update the on-highway CH4 and N2O emission factors is written clearly and
transparently. The methodology, data and assumptions used in the update are presented in an organized,
concise manner and they are we 11-documented by statistical analyses included in the appendices.

Response: EPA appreciates the feedback.

Comment: Possible Typo or Transcription Error

Pgs. 2-3, Tables 2 and 3: the ~+7-fold increase in HDGV CH4 emissions due to the use of "new" versus
"current" emission factors that is shown in Table 3 is extremely surprising (and very suspect) given the
general reduction in methane emission factors (on the order of 0-76%) for this vehicle category that is
shown in Table 2. Is this a typo or transcription error? Are there other factors that accompanied the use of
updated emission factors (e.g., changes in activity, vehicle population, etc.) that have not been explained?

Response: Thank you for identifying a critical typo in Table 3. The "current" CH4 emissions for
HDGVs should be 1,551 metric tons, not 23,383 metric tons. The results presented in Table 3 reflect
changes to emission factors only (i.e., vehicle population and activity inputs are held constant).

Chapter 4. Industrial Processes and Product Use
(IPPU)

4.17 Iron and Steel Production and Metallurgical Coke Production

Comment: Subchapter is Disjointed and Terms Need Defining

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I find this subchapter to be somewhat disjointed. In its opening remarks, it would be best to explain that
"pig iron" is the common, but unfortunate term used for what would be better described as "crude iron".
Pig iron is really that (small fraction currently; a large fraction 50-100 years ago) subset of crude iron
production that is actually poured into small molds to form "pigs". The current interchangeable use of
"pig iron" for "crude iron" can lead to problems with the foreign literature/statistics. For example, some
years ago, the USGS data on Turkish crude iron output was erroneously revised downwards from, if
memory serves, c. 5 Mt/yr. to something like 250,000 MT/year, because the then country specialist (the
late Phillip Mobbs) had found a Turkish Govt, reported data series for pig iron. What he had found was a
longstanding series for "pik demir" (which is the iron cast into pigs), whereas what he should have
(continued to have) used was the reported series for "ham demir" (crude iron). When the error was
pointed out to Mr. Mobbs, he revised the data back to the larger number series.

Most of the CO2 released in iron & steel production is from the production of crude iron; although the
chapter does mention this here and there, the main impression is that the focus is on crude steel
production.

In blast furnaces, the CO2 largely comes from the use of coke and the carbonate flux (really, it's a
slagging agent, although "flux" will suffice). The use of flux seems not to be dealt with except indirectly.
Mention is made of a deduction (from Other Carbonate Uses) to avoid double-counting of the flux used in
steel production, but in reality, you should say "...in crude iron production". It is the blast furnace that
uses limestone and/or dolomite. Steel furnaces use LIME as a flux, and this use should not release any
additional CO2 (the manufacture of lime, of course, is dealt with in a separate chapter); most U.S.
integrated plants, and all independent EAF plants, buy their lime from the lime industry.

In making crude iron in a blast furnace, you will consume c. 0.2 - 0.5 t of carbonate slagging agent
(limestone and/or dolomite) per ton of crude iron produced, which would thus yield approx. 0.1-0.21 of
CO2 per ton of iron; the net calculation (all sources) would be debited for carbon (c. 4%) remaining in the
crude iron. Then the subsequent steel furnace will burn off most of this carbon in the crude iron feed; an
EAF may burn some C-electrode to add carbon to the melt if it overburned the melt's carbon by mistake.

If you are going to mention the number (11) of iron and steel (integrated) complexes, it would be of
interest to note that there were 21 active blast furnaces (only) in 2015 at these plants—a sad decline...

Section 24 (Iron and Steel Production) is introduced by talking about the minor stuff (sinter, DRI, pellets)
rather than the major outputs of crude iron and crude steel.

In the first para of section 4-25; add "carbonate fluxes or slagging materials" to the list of inputs to the
blast furnace.

In the 2nd para (line 12), fluxes appears as an input for steel production; again, for steel production, the
flux is lime, not carbonate, and will not yield CO2 in the steel furnace. The confusion is continued in lines
15-17 where carbonates are linked to steel manufacture instead of to crude iron production.

Table 4-29 would be more useful if you split the inputs in terms of those for crude iron production (blast
furnace) from those for crude steel production (steel furnace).

Table 4-31 needs a data series for flux (slagging agent) consumption for the blast furnaces. It is unclear if
any of this (carbonate) flux was put in the EAF and BOF sections; if so, it should be removed. The EAF
and BOF flux of interest is lime. However, be aware that some data for "fluxes" for BFs includes silica
sand (which is a flux, but yields no CO2).

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Response: EPA has updated background descriptions to improve the explanation of current
production processes and to clarify the use of the terms "pig iron" and "crude iron" in the upfront
section of the source category text. This update is to reflect the iron and steel emissive processes, the
status of the industry, and changes over the time series. For the current inventory (i.e., 1990
through 2016), EPA has not implemented updates to Table 4-31 to include slagging agent
consumption for blast furnaces. EPA will need to assess available data and review appropriate
emission factors per the 2006 IPCC Guidelines before including in future reports.

Chapter 6. Land Use, Land Use Change and
Forestry (LULUCF)

Comment: Chapter is Clear

We find the chapter to be clear, transparent, concise, understandable, and thoroughly documented. The
basic methodology and data sources are sound and have remained mostly unchanged. EPA is using
appropriate data for components of this chapter, and the forest inventory data which forms the basis for all
forest carbon stock estimates is undergoing steady improvement with thorough scientific review.

Response: EPA appreciates the commenter's feedback on clarity and transparency of Chapter 6 of
the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016.

6.1 Representation of the US Land Base

Comment: Question about Availability of Citations

I hope the citations that are described as "in prep" are available to reviewers within the coming year?
Especially on page A-207, Theoretical age class transition matrix, Wear and Coulston in prep.

Response: Most of the references listed as in prep on page A-207 are published, the figure will be
updated with the correct citations in the final Inventory published in April 2018.

Comment: Question about FIA Data Table

I can appreciate the approach to not greatly update the inventories every year, and instead go to biennial
reporting. It is a great deal of work to update the inventories.

My main comment is about Table 6-3. If FIA data are not used for forests in Alaska, (top part of table), it
is hard to believe it is used in the croplands, grasslands, other lands, settlements, and wetlands for Alaska
(bottom part of table, two dots in the FIA column). And how does this table relate to the presentation of
the USGS numbers for Alaska? (See table 6-10).

Response: The table (listed as 6-3 in Expert Review version) will be updated to indicate that FIA
was used to determine land area for portions of Alaska. The chapter text already indicates this is
the case. This table is not used directly in presentation of the USGS numbers for Alaska as shown
in the Forest Land Remaining Forest Land section, but the outputs from the Land Representation
analysis for Alaska is overlaid on the USGS spatially explicit estimates for Alaska to approximate
the area of managed land and thus the "anthropogenic" emissions.

Comment: Recommendation of a New Source

For US territories, a new publication has just been released based to a large degree on FIA data that states
deforestation is not much of an issue in the islands. Would be worth a look, and perhaps citing.

However, it doesn't include the most recent surveys from some of the islands. See Assessing Forest
Sustainability in the Tropical Islands of the United States at the link below.

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https: //www .fs. fed .us/re search/sustain/sustainability-reports .php#tabs-2

Response: EPA will review the publication and when resources allow for inclusion of US
Territories, EPA will utilize this to assist in developing estimates of GHG emissions/removals from
these territories.

6.2 Forest Land Remaining Forest Land

Comment: Parenthesis Needed

Typo: 6-31, line 1 - parenthesis missing after A-99

Response: EPA has included the noted missing parenthesis.

Comment: Change from 2015 Inventory Supported

We support the decision to move to a biennial compilation schedule, using land area data from the prior
inventory (2015) for this report. This is a reasonable compromise to obtain accurate estimates while
focusing efforts on other improvements, given the large area of the US land base and the relatively slow
rates of change. This is well documented in the methodology sections.

Response: EPA appreciates the commenter's feedback on the recent implementation of the biennial
compilation process with the goal of directing resources to planned improvements for this source
and enhancing the overall clarity and transparency of the methodology for Forest land Remaining
Forest Land estimates in Chapter 6 of the Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2016.

Comment: Recent Improvements on Methodology are Successful

Recent improvements to the report methodology have made for a more comprehensive inventory,
reflecting more land areas, all carbon pools, and providing better resolution on land area changes.
Especially notable is the beginning of collection of inventory data for interior Alaska. When complete,
this will add important information to the inventory.

Response: EPA appreciates the commenter's feedback supporting the recent improvements to
estimates for Forest land Remaining Forest Land in Chapter 6 of the Inventory of U.S. Greenhouse
Gas Emissions and Sinks: 1990-2016.

Comment: Planned Improvements Supported

The planned improvements for Forest Land remaining Forest Land are well considered. We support the
use of remotely sensed data for improving spatial and temporal scale of change data, following scientific
review of methods. We also strongly support the dissemination of open source code for transparency in
computations. More consistency in soil depth used for soil carbon reporting for land use changes is a
worthwhile planned improvement.

Response: EPA appreciates the commenter's feedback supporting planned improvements to
estimates for Forest land Remaining Forest Land in Chapter 6 of the Inventory of U.S. Greenhouse
Gas Emissions and Sinks.

6.8 Wetlands Remaining Wetlands

Comment: Changes Needed to Synthesize Wetland Fluxes

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It is clear that work remains to improve the inventory information on wetland changes. Identification of
types of transition of lands into and from coastal wetland categories would be informative. In addition,
some summarization of fluxes for the overall wetlands category would be beneficial; it is difficult to
determine from the present format the total flux from wetlands remaining wetlands and lands converted to
wetland as no summary table is presented. Fluxes for peatlands, vegetated wetlands, and un-vegetated
wetlands and transitions among them are presented separately, making it difficult to synthesize
information on overall wetland fluxes.

Response: EPA appreciates the commenter's feedback on [additional] planned improvements to
consider for Wetlands Remaining Wetlands in Chapter 6 of the Inventory of U.S. Greenhouse Gas
Emissions and Sinks. Improvements to the Wetlands section to better represent land use and
transitions in the Wetlands category are planned for a future inventory, primarily by integrating
the Coastal Change Analysis Program (CCAP) data into the land representation analysis. EPA will
also evaluate how to improve the presentation of the Wetlands Section to provide a better summary
of the fluxes from this chapter.

6.10 Settlements Remaining Settlements

Comment: Clarity in Estimates are Underway

As noted in the report, improvements in distinguishing urban forest estimates from the rest of the forest
inventory are underway, and will provide clarity in estimates pertaining to settlements remaining
settlements as well as relevant transitions to and from the settlement category.

Response: EPA appreciates the commenter's feedback supporting planned improvements for
estimating Settlements Remaining Settlements in Chapter 6 of the Inventory of U.S. Greenhouse
Gas Emissions and Sinks: 1990-2016.

6.10 Settlements Remaining Settlements - Changes in Yard Trimmings
and Food Scrap Carbon Stocks in Landfills

Comment: Description of Food Waste

Overall -1 think that the methodology is clear and transparent and applaud EPA for the document's
preparation.

Page 103: In describing the amounts of yard trimmings and food waste that are generated, I always use
the word "estimated" as opposed to writing the text as if these quantities are definite. This is especially
important in the case of food waste. The EPA considered food waste from sources that are defined as
MSW only and does not include food waste that is generated at commercial food processing facilities
(e.g., a factory that cans tomatoes or oranges). As such, the estimate of food waste to landfills is likely
low.

Response: EPA agrees that clarification is helpful and has edited the text to reflect that the values
are estimated and not definite. Yard trimming and food scrap generation data are obtained from
EPA's Advancing Sustainable Materials Management: Facts and Figures report, "Table 1.
Generation, Recycling, Composting, Combustion with Energy Recovery and Landfilling of
Materials in MSW". These MSW values include waste from residential, commercial, and
institutional sources.

Comment: Improvement for Methodology Needed
Page 104 - Methodology

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This methodology captures food and yard waste present in MSW only. There are other sources. As noted
above, in the case of food waste, there is commercial generation. In the case of yard trimmings, some
debris from road construction is also disposed in dedicated landfills (I do not have detailed information
but am told, for example, that the state Departments of Transportation operate "stump dumps" that
received large trees.

Response: EPA agrees, but has not identified data sources to quantify the food scraps from
commercial sources or relevant debris from road construction for inclusion in estimating
emissions/removals from landfilled, yard trimmings and food scraps, and have therefore not
included these in the current estimates. EPA will continue to search for these data and add this to
our list of planned improvements, noting that the commenter did not include any specific data
sources to include these sources in the current Inventory report.

Comment: Clarification of Decay Rates
Page 104 - Methodology

To clarify one item on the decay rates. The individual waste component decay rates that are given in de
la Cruz and Barlaz (2010) for a bulk MSW decay rate of 0.04 can be readily adjusted to waste component
decay rates for any other desired bulk MSW decay rate as follows:

Individual component decay rate at bulk decay rate of 0.03 = Individual component decay rate at bulk
decay rate of 0.04 * 0.03/0.04

I think that EPA is aware of this but wanted to be sure.

Response: EPA appreciates this feedback and will add this review to the planned future
improvements the clarification on the decay rates and update the factors as appropriate following
our review in future reports.

Comment: Recommendation for Planned Improvements
Page 109 - Planned Improvements

It might be possible to consult with agronomists and get estimates of the mass of grass that grows per acre
on residential lawns as a function of climate. This would provide a bottom up estimate of total grass
generation that could be compared with the EPA methodology.

Response: EPA will add commenter's suggestion to the list of planned improvements to determine a
total residential lawn grass generation for sake of comparison to our methodology as category-
specific QC step per IPCC good practice to implement for future reports.

Comment: Inconsistent Decay Rates

Table 6-76: The Decay Rates here do not match the values in de la Cruz and Barlaz. I think this is
because the decay rates in Table 6-76 are weighted average rates across the US based on different regions
with different bulk MSW decay rates. If I am correct, I suggest an explanatory note in Table 6-76.

Response: EPA has included a note in Table 6-81, Section 6.10 of the Public Review version of the
report stating that "the decay rates are presented as weighted averages based on annual
precipitation categories and population residing in each precipitation category".

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Comment: Attached Recommended Sources

Over the past several years, my group has published a number of papers on the biodegradability of wood.
I am attaching those papers for your convenience. I do not think that they are necessarily of immediate
use, but do think they provide some useful background for future work.

Response: EPA appreciates this information and will review the papers in consideration with other
planned improvements to consider how they can improve our methods for future estimates.

Comment: Consistency Needed for Storage Factors

Finally, I agree with the comment that ultimately, we need to make the methane yields and C storage
factors internally consistent. We have done this and adjusted methane yields accordingly in the following
manuscript (Table S5).

Response: EPA will review the paper (Hodge, K. L., Levis, J. W., DeCarolis, J. F. and M. A. Barlaz,
2016, "Systematic Evaluation of Industrial, Commercial, and Institutional Food Waste
Management Strategies in the U.S," Env. Sci. and Technol., 50,16, p. 8444 - 52) provided and will
evaluate the potential to make adjustments to the inventory methodology for future inventory
reports.

Chapter 7. Waste

7.1 Landfills

Comment: Approval of Updated Approach for MSW Landfills

We have been very pleased with the cooperative effort among EPA and stakeholders to review and update
the approach used to estimate greenhouse gas (GHG) emissions at MSW landfills and we look forward to
continuing to work with you towards further improvements. The landfill sector strongly supports the
Agency's efforts thus far to update the inventory, and particularly your decision to use Greenhouse Gas
Reporting Program (GHGRP) data in the most recent inventory. We strongly support continued use of
this data.

These data are more reliable and accurate for estimating nationwide emissions from MSW landfills. In
previous comments on this issue, we explained why using GHGRP data is the preferred approach.

• The MSW landfill sector (Subpart HH) emissions data are significantly more detailed and up-to-
date than the estimation approach used in previous GHG Inventories;

• Every MSW landfill reporting to Subpart HH is subject to annual validation via EPA review of
submitted data - a level of scrutiny that does not occur in the GHG Inventory;

Each MSW landfill that reports under Subpart HH has a "designated representative," who must certify -
under penalty of law - that the data submitted by the site are accurate and developed in accordance with
regulatory requirements. These data are developed using consistent, EPA-approved methods, and are
certified by reporters and independently quality-assured by EPA, which ensures transparent and reliable
data for use in emissions estimates.

Response: EPA appreciates the commenter's feedback supporting improvements applied for
estimating emissions from Landfills in Chapter 7 of the Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990-2016.

Comment: The Scale-Up Factor for MSW Landfills

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We thus recommend that EPA recalculate the scale-up factor using Option (a) and an adjusted WIP
amount that is at least 60 percent lower than the amount assumed in the Agency's previous calculation.
EPA's assessment of non-reporting MSW landfills shows that the GHGRP captures the vast majority of
emissions from the MSW landfills and a scale-up factor of no greater than 5 percent would be far more
appropriate for use in the Inventory.

Full Context: Recognizing that the GHGRP does not include every MSW landfill in the country - (MSW
landfills that ceased taking waste prior to 1980 or have potential emissions less than 25,000 tons CC^e) -
we supported EPA's decision to use a scale-up factor to estimate emissions from non-reporting landfills
in the 2017 Inventory. EPA calculated a scale-up factor of 12.5%, based on the percent difference
between the 1990-2014 Inventory emissions and the GHG emissions as reported for 2010-2015 and back-
casted emissions for 2005 to 2009. We were, however, concerned that the scale-up factor of 12.5%
would be overly conservative, and recommended that a factor of 10% would be sufficient to avoid
underestimating emissions. We also encouraged EPA to reassess an appropriate scale-up factor to more
accurately account for non-GHGRP reporting landfills.

EPA has endeavored to do so by developing a draft list of MSW landfill facilities that do not report to the
GHGRP by comparing the Agency's GHGRP database with the LMOP 2017 database and the Waste
Business Journal (WBJ) 2016 database. This exercise has been fraught with difficulty due to the variety
of facility names that may be associated with an individual landfill, the incorrect latitude and longitude
values assigned to many landfills and the possible inclusion of non-MSW landfill sites in both the LMOP
and WBJ datasets. EPA asked the landfill sector for assistance in reviewing the draft list.

Because the analysis of almost 1,800 landfill sites would be very time-consuming, the landfill sector
focused its review on those landfills on the list with the greatest amount of waste-in-place. Waste-in-
place is the primary variable for calculating potential emissions from a landfill. The landfill sector
reviewed approximately a quarter of the sites on the draft list and found significant errors. Many of the
sites were identified as reporting into the GHGRP, so their emissions were already captured. Other sites
were misidentified as MSW landfills, and still other listed sites were duplicates and therefore accounted
for multiple times.

The landfill sector1 reviewed a total of 450 sites on the EPA's list of non-reporting MSW landfills. The
below table summarizes the results of our review.

Summary of Review

450

Total Sites Checked

Duplicates

EXEMPT - NOT MSW landfills

287

Non-Reporting MSW landfills

147

Reporting-MSW landfills in
GHGRP

3,057,855,595

EPA Total Forced WIP in tons for
non-reporting sites

1,137,266,189

Industry Adjusted Forced WIP in
tons for non-reporting sites

37.91%

% of Total

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In adjusting the total forced WIP for remaining MSW landfills, the landfill sector removed only the WIP
associated with non-MSW landfills (and those sites that are already reporting WIP and emissions through
the GHGRP. Adjusting the WIP for this subset of landfills in the spreadsheet reduces the total WIP by
more than 60 percent.

Developing an accurate list of non-reporting MSW landfills and the associated WIP is essential to both
options the Agency has considered for calculating a scale-up factor.

a) The percentage difference in total waste-in-place between the non-reporting facilities and the GHGRP
MSW landfill facilities; or

b) The percentage difference in net methane emissions between the non-reporting facilities and the
GHGRP MSW landfills.

Using its draft list on non-reporting landfills, EPA determined that Option (a) yields a scale-up factor of
approximately 11%, as shown in Table 1 of the October 16, 2017 EPA Expert Review memo. This value
was determined from the estimated total waste-in-place for non-reporting facilities compared to facilities
reporting to the GHGRP. To calculate GHG emissions for non-reporting facilities, 11% of the total
GHGRP emissions for each year of the time series would be applied.

Option (b) yielded a scale-up factor of approximately 26%, as shown in Table 2. This value was
determined from estimated methane emissions for the non-reporting landfills. EPA used the Inventory
Waste Model (first order decay methodology) and estimated annual waste disposal data that excludes an
average amount of C&D and inert waste, and the same default factors as applied in previous inventories
for DOC, MCF, etc., and a 10 percent oxidation factor.

Leaving aside the fundamental flaws with the EPA list of non-reporting landfills, the landfill sector
recommends that Option (a) is the more appropriate approach because waste-in-place data are readily
available and are more reliable than modeled net emissions. Specifically, Option (a) relies on available
waste acceptance data to determine waste-in-place for the non-reporting facilities and waste-in-place data
reported under the GHGRP for MSW landfills reporting under Subpart HH. Option (b), in contrast, relies
on the first order decay methodology, as well as many default factors that may not be appropriate across
the country.

We thus recommend that EPA recalculate the scale-up factor using Option (a) and an adjusted WIP
amount that is at least 60 percent lower than the amount assumed in the Agency's previous calculation.
EPA's assessment of non-reporting MSW landfills shows that the GHGRP captures the vast majority of
emissions from the MSW landfills and a scale-up factor of no greater than 5 percent would be far more
appropriate for use in the Inventory.

1 - SWANA members in state chapters across the country; major, private landfill owner/operators who are
members of NWRA; SCS Engineers and Weaver Consulting, which conduct GHG Reporting for many
public and private sites, and WM and Republic Services.

Response: EPA appreciates the commenter's feedback supporting planned improvements for
estimating emissions from landfill in Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2016. EPA also appreciates the effort undertaken by the landfill industry to
review the list of landfills that do not report to the GHGRP and the attempt to remove reporting
landfills and duplicates, as well as fill in missing waste-in-place and open/closure year data where
available. Based on further review within EPA and industry input, EPA has revised the scale-up
factor used in the emissions estimations for 2004-2016 in the time series from 12.5% to 9%. Please

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refer to the Recalculations Discussion in Section 7.1 of the Inventory text as well as the supporting
memo "Methodological refinements as applied in the 1990-2016 estimates of U.S. greenhouse gas
emissions from MSW landfills to account for emissions from facilities not reporting to the
Greenhouse Gas Reporting Program" from Kate Bronstein and Meaghan McGrath of RTI
International to Rachel Schmeltz of EPA/CCD, April 4, 2018 for more detail on the steps taken to
refine the scale-up factor.

Comment: The Scale-Up Factor for MSW Landfills

1) Additional datasets to generate and/or refine a list of non-reporting landfills.

Both EPA and the landfill sector have spent considerable time attempting to create a useable database of
non-reporting landfills based on EPA's LMOP and WBJ databases. There are no other datasets to
evaluate. This effort has been difficult and time-consuming for many reasons, including problems in
identifying non-reporting landfills, tracking down landfills with addresses but incorrect LAT/LONG
coordinates and confirming that GHGRP, C&D, and industrial landfills are not in the non-reporting
landfill database. Significant effort was undertaken by the landfill sector to review and revise the list of
non-reporting landfills. With additional time, we believe we could further refine the list. However, our
review to date of the Agency's database of non-reporting landfills has eliminated over 60 percent of the
total waste-in-place used to calculate the Agency's initial scale-up factors of 11% and 26%. We
recommend the Agency recalculate the scale-up factor using Option (a) and a reduced WIP amount that is
at least 60 percent less than that used in the prior calculation.

Response: EPA appreciates the commenter's feedback confirming that there are no additional
datasets to use in informing the scale-up factor applied to estimating emissions from MSW landfills
in Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016. EPA also
appreciates the effort undertaken by the landfill industry to review the list of landfills that do not
report to the GHGRP and the attempt to remove reporting landfills and duplicates, as well as fill in
missing waste-in-place and open/closure year data where available. Based on further review within
EPA and industry input, EPA has revised the scale-up factor used in the emissions estimations for
2004-2016 in the time series from 12.5% to 9%. Please refer to the Recalculations Discussion in
Section 7.1 of the Inventory text as well as the supporting memo "Methodological refinements as
applied in the 1990-2016 estimates of U.S. greenhouse gas emissions from MSW landfills to account
for emissions from facilities not reporting to the Greenhouse Gas Reporting Program" from Kate
Bronstein and Meaghan McGrath of RTI International to Rachel Schmeltz of EPA/CCD, April 4,
2018 for more detail on the steps taken to refine the scale-up factor.

Comment: The Scale-Up Factor for MSW Landfills

2) How to handle landfills that "off-ramp" from the GHGRP.

The first reporting year for Subpart HH (and other subparts) was 2010, and the latest reporting year is
2016. To date, 16 landfills (out of 1137 in 2015) have met the criteria for exiting the GHGRP reporting
requirements, representing merely 1.4% of the landfills reporting under Subpart HH. Given the very
small number of landfills that have stopped reporting, we find it unnecessary and a very poor use of
Agency resources to develop a new approach for accounting for these landfills' emissions. The potential
effect of these emissions is tiny, particularly considering the revisions to the dataset of non-reporting
sites, and the uncertainties and errors introduced using the first order decay model and non-representative
DOC values. Further, EPA has the historical data for the "off-ramp" sites and most if not all the "off-
ramp" sites are closed landfills where emissions will continue to decline overtime.

Response: EPA appreciates the commenter's assessment of the utility of developing an approach to
account for emissions from landfills that have stopped reporting to the GHGRP because they met

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the "off-ramp" provisions (i.e. reported less than 15,000 metric tons of CO2 equivalent for 3
consecutive years or less than 25,000 metric tons of CO2 equivalent for 5 consecutive years). While
the data reported by these facilities in previous reporting years is incorporated into the scale-up
factor analysis, no separate approach has been developed. EPA will periodically assess the impact
these off-ramping facilities may have on emissions estimates to ensure national estimates are as
complete as possible.

Comment: The Scale-Up Factor for MSW Landfills
3) What is the best approach for applying a scale-up factor?

EPA is currently applying the same scale-up factor for 2005 to 2016, but is considering whether it would
make more sense to apply a scale-up factor to blocks of time (e.g., 5 years), annually, and/or when
GHGRP facilities off-ramp.

The landfill sector does not see the value in applying the scale-up factor at such a detailed level, given the
significant reduction in the potential impact of non-reporting landfills to nationwide emissions, and the
small number of landfills likely to either drop below the threshold for reporting or reach the Subpart HH
threshold for reporting. This represents a poor use of the Agency's limited resources.

Response: EPA appreciates commenter's input on the application of the scale-up factor as applied
to estimating emissions from MSW landfills in Chapter 7 of the Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990-2016.

Comment: Degradable Organic Carbon (DOC)

Conclusion: Based on EREF's research, we urge EPA to update the DOC values to reflect significant
changes in the amounts and types of organic materials being landfilled over the last several years. The
values now in use are inaccurate and should not be used going forward. We request that EPA review and
update the DOC values in the next version of the GHG Inventory.

Full Context: In 2016, the Environmental Research and Education Foundation (EREF) undertook a state-
based study of DOC values for both MSW Only Landfills and Non-MSW Material going to MSW
Landfills. The DOC guideline recommended by EPA for MSW Only Landfills is 0.31 and the
recommended guideline for Non-MSW material going to MSW landfills is 0.20. As described below,
these guidelines over-estimate the amount of organic waste deposited in landfills, which results in
inaccurate estimates of landfill gas generation and methane emissions. We note that neither of the
recommended DOC guidelines have been reviewed by EPA in many years, and we support EPA's view
that it is time to update the DOC values.

EREF reviewed recent waste composition studies for MSW Only Landfills conducted by 13 states and
confirmed that waste composition has and continues to change overtime, as fewer organic materials are
sent to MSW landfills. In fact, the EREF results show that the percent of the MSW-only stream that is
organic waste ranged from 50.1% to 69.4%, with an average of 60.2% (Table l).2 EPA data also indicate
that the fraction of organics going to landfills generally declined from 1994 to 2009. Quoting EREF:

Subsequent analyses were performed using both state characterization study data and EPA Facts and
Figures data to compute DOC values for MSW (DOCMSW). An average DOCMSW of 0.184 was
computed from the state study data, with values ranging from 0.142 - 0.209. All characterization studies
had DOCMSW values significantly less than the default value of 0.31, which suggests this value is not
representative of real-world conditions for MSW (Table 2; Figure 4). Analysis of U.S. EPA data ... also
results in a significantly lower DOCMSW value compared to the U.S. EPA guideline of 0.31, with

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DOCMSW values ranging from 0.218 in 1994 to a minimum of 0.165 in 2011 (Figure 4; Appendix B).
Both the state characterization studies and U.S. EPA Facts and Figures data independently suggest that a
DOC guideline value of 0.31 for MSW is not representative of the landfilled MSW stream.

The use of a single DOC value as a guideline for all U.S. landfills makes the implicit assumption that
waste composition does not change overtime or due to location. The results presented here suggest these
are not valid assumptions and that, collectively, the use of a static DOC value of 0.31 may lead to
inaccurate estimates of landfill gas emissions for landfills that only accept MSW. Because this specific
analysis is focused only on MSW materials, one would expect the inclusion of non-MSW materials going
to a landfill to impact DOC estimates even more.3

With respect to Non-MSW going to MSW Landfills, EREF finds "a common assumption is that all waste
materials entering MSW landfills consist only of MSW materials. As noted previously, MSWLFs rarely
accept MSW exclusively. Rather, most MSWLFs (landfills in 45 states) are authorized to accept other
Subtitle D wastes in addition to MSW."4 In addition, EREF notes:

Given that a third of incoming waste to MSWLFs consists of non-MSW materials, there is significant
potential for non-MSW materials to impact the relative fraction of organics and degradable organic
carbon (DOC) of the MSWLF waste stream.5

The amount and types of non-MSW Subtitle D organic wastes impact the DOC value for the landfilled
waste since it consists of both MSW and non-MSW streams. This combined DOC value (DOCSubD)
incorporates degradable organic carbon from all Subtitle D wastes accepted at MSWLFs (both MSW and
non-MSW). ... State waste characterization studies were used to estimate the relative fraction of each
organic constituent for C&D and industrial waste ... and DOC for each waste type was calculated using
Equation lb. Based on this analysis the DOCSubD value of landfilled waste is 0.161 (Table 6)."6

EREF also highlights that the DOCSubD value is lower than the guideline value of 0.20 for bulk waste. It
is also lower than the average DOCMSW value of 0.184 computed in the prior section, indicating the
inclusion of non-MSW decreases overall DOC. Using the same approach as for the DOCMSW analysis,
state-specific organics content and DOCSubD values for all fourteen states with sufficient data were
determined and presented in Table 7, below. The results, all for 2013, highlight differences in DOCSubD
based on locale and suggest the use of a static 0.20 guideline for bulk waste may lead to inaccurate
estimates of methane generation and emissions, especially in some areas.7

Thus, EREF concludes as follows:

The average computed DOC value for MSW using state data was 0.184, or roughly three-fifths of the
MSW guideline value. The average computed DOC value for bulk waste using state data was 0.161, or
roughly four-fifths of the bulk waste guideline. This analysis suggests that the U.S. EPA's guideline
DOC values of 0.31 for MSW-only landfills and 0.20 for facilities accepting non-MSW Subtitle D wastes
overestimate DOC at these landfills and may result in inaccurate estimates of landfill gas generation and
methane emissions.8

Based on this review of the DOC values for MSW landfills, the landfill sector concludes that the long-
standing DOC values developed in the past are inaccurate and are likely to over-estimate both landfill gas
generation and methane emissions. The data provided by EREF confirms that two trends are driving the
changes at MSW landfills. First, many MSW landfills are handling less organic matter now, and this
trend is anticipated to continue due to state and local organics diversion goals, and second, the increase of
Subtitle D non-MSW waste disposed has altered the DOC for all waste deposited in MSW landfills.

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Based on EREF's research, we urge EPA to update the DOC values to reflect significant changes in the
amounts and types of organic materials being landfilled over the last several years. The values now in use
are inaccurate and should not be used going forward. We request that EPA review and update the DOC
values in the next version of the GHG Inventory.

2 - Staley, B.F. and Kantner, D.L., Estimating Degradable Organic Carbon in MSW Landfills and the
Impact ofNon-MSW Materials, EREF - Environmental Research and Education Foundation, 2016, Table
!p. 4.

3 Ibid. pp. 6 - 7

4 Ibid. p. 8

5 Ibid. p. 10

6 Ibid. p. 11

7 Ibid. p. 12

8 Ibid. p. 13

Response: As stated in the Planned Improvement section of Section 7.1 of the Inventory of U.S.
Greenhouse Gas Emissions and Sinks: 1990-2016, the Inventory currently uses one value of 0.20 for
the DOC for years 1990 to 2004. With respect to improvements to the DOC value, EPA developed a
database with MSW characterization data from individual studies across the United States. EPA
will review this data against the Inventory time series to assess the validity of the current DOC
value and how it is applied in the FOD method. Waste characterization studies vary greatly in
terms of the granularity of waste types included and the spatial boundaries of each study (e.g., one
landfill, a metro area, statewide).

Comment: The k Factor (Methane Generation Rate Constant)

On page 25 of the U.S. Greenhouse Gas Inventory: Update on Methodology Improvement for MSW
Landfills,9 EPA notes that it is using k-values based on climate. Estimation of the CH4 generation
constant (k) is a function of a variety of factors, including moisture, pH, temperature, and other
environmental factors, and landfill operating conditions."10 For many years, EPA has used three k
values, disaggregated by climate: 0.02 [dry climate], 0.038 [moderate climate], and 0.057 [wet climate].

We are concerned that these k-values are outdated and rife with uncertainty, as confirmed by the Draft AP
42.2.4 Municipal Solid Waste Landfills, which states:

There is a significant level of uncertainty in Equation 2 and its recommended default values for k and Lo.
The recommended defaults k and Lo for conventional landfills, based upon the best fit to 40 different
landfills, yielded predicted CH4 emissions that ranged from -30 to 400% of measured values and had a
relative standard deviation of 0.73 (Table 2-2). The default values for wet landfills were based on a more
limited set of data and are expected to contain even greater uncertainty.11

As noted above, the landfill sector has previously highlighted the significant issues with the k values used
in the Draft AP-42 Section 2.4: Municipal Solid Waste Landfills. In fact, EPA has never finalized AP-42
for MSW landfills, despite the k-value issues identified by EPA in both AP-42 and the Background
Information Document. With uncertainties in CH4 emissions ranging from -30% to 400% under EPA's
assessment of the LandGEM model, it is difficult to take these data seriously. For this reason, we again
urge EPA to review and resolve the significant problems in the k value data set.

9 U.S. EPA, U.S. Greenhouse Gas Inventory: Update on Methodology Improvements for MSW Landfills,
August 16, 2017.

10 U.S. EPA, Draft AP 42.2.4: Municipal Solid Waste Landfills, October 2008, p. 2.4-6.

11 Ibid.

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Response: As stated in the Planned Improvement section of Section 7.1 of the Inventory of U.S.
Greenhouse Gas Emissions and Sinks: 1990-2016, in a future Inventory cycle, EPA will review the k
values for the three climate types (dry, moderate, and wet) against new data and other landfill gas
models, and how they are applied to the percentage of the population assigned to these climate
types. EPA will also assess the uncertainty factor applied to these k values in the Waste Model. A 30
percent uncertainty factor is applied to each k value in the Monte Carlo analysis, which is
consistent with that recommended by the IPCC (2006).

Comment: The 10 Percent Oxidation Factor

For the period 1990 - 2004 in the inventory time series, a national estimate of methane generation and
emissions are calculated using a combination of secondary data sources that detail the annual quantity of
waste landfilled and the annual quantity of methane recovered from facilities with landfill gas collection
and control systems. EPA applies a 10% oxidation factor to all facilities for the years 1990 to 2004.

We understand that EPA is considering revisions to the value of the oxidation factor and possibly
including two oxidation factors: one for waste disposed at facilities with landfill gas collection and
control systems (GCCS), and the other for landfills without GCCS. EPA acknowledges that the Agency
has not developed a way of assigning a percentage of waste disposed in landfills with gas collection or
without for those years.

While assigning different methane oxidation values to landfills with and without gas collection systems
may seem to be a valid concept, that one site variable should not be applied to all sites in the inventory
universe as THE defining characteristic affecting methane flux and oxidation. Other site-specific landfill
attributes are important in assessing methane oxidation potential (e.g., WIP, modeled CH4 generation,
cover area and cover type). Sites with gas collection might have lower methane flux into the cover and
thus would be expected to have higher rates of oxidation due to this lower flux. However, applying this
one characteristic to all landfills in the Inventory without respect to their other site-specific attributes will
not provide a valid, nationwide analysis. Many sites in the Inventory are small or older sites with low gas
generation rates and low methane flux. They would still be expected to have oxidation rates that exceed
10% even without gas collection systems. So, the information needed to provide an accurate estimate of
methane oxidation goes beyond simply knowing whether the site employs gas collection or not.

Response: EPA appreciates commenter's input on the oxidation factor as applied to estimating
emissions from MSW landfills in Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2016. As stated in the Planned Improvement section of Section 7.1 of the Inventory,
EPA is continuing to investigate options to adjust the oxidation factor from the 10 percent currently
used for 1990 to 2004 to another value or approach such as the binned approach used in the
GHGRP (e.g., 10 percent, 25 percent, or 35 percent based on methane flux. The oxidation factor
currently applied in the later portion of the time series (2005 to 2016) averages at 19.5 percent due
to the use of the GHGRP data while the earlier portion of the time series applies the default of 10
percent.

Comment: The 10 Percent Oxidation Factor

1) Available data sources to address trends in installation of landfill gas collection systems.

The landfill sector is not aware of sources that would provide information on the extent of landfill gas
collection within the industry or the trends in gas system installation outside of the reporting landfills in
the GHGRP. The EPA LMOP dataset only indicates whether a landfill has a gas collection system, but
does not note the date of installation or expansion.

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Response: EPA appreciates commenter's input and takes note that the commenter is not aware of
any data sources to address trends in installation of landfill gas collection system. As stated in the
Planned Improvement section of Section 7.1 of the Inventory, EPA is continuing to investigate
options to adjust the oxidation factor from the 10 percent currently used for 1990 to 2004 to
another value or approach such as the binned approach used in the GHGRP (e.g., 10 percent, 25
percent, or 35 percent based on methane flux). The oxidation factor currently applied in the later
portion of the time series (2005 to 2016) averages at 19.5 percent due to the use of the GHGRP data
while the earlier portion of the time series applies the default of 10 percent.

Comment: The 10 Percent Oxidation Factor

2)	Appropriate oxidation factors for landfills with and without landfill gas collection systems.

The landfill sector does not think that it is appropriate to assign oxidation factors to a landfill based solely
on whether it operates a GCCS. As explained above, other site-specific landfill attributes, such as WIP,
type and extent of cover and modeled methane generation are also important factors in assessing potential
methane oxidation. Developing an accurate estimate of methane oxidation is significantly more
complicated than relying on whether the landfill has a gas collection system.

Response: EPA appreciates commenter's input on the oxidation factor as applied to estimating
emissions from MSW landfills in Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2016 and that the existence of a GCCS is not the sole factor in estimating the amount of
methane oxidation. As stated in the Planned Improvement section of Section 7.1 of the Inventory,
EPA is continuing to investigate options to adjust the oxidation factor from the 10 percent currently
used for 1990 to 2004 to another value or approach such as the binned approach used in the
GHGRP (e.g., 10 percent, 25 percent, or 35 percent based on methane flux). The oxidation factor
currently applied in the later portion of the time series (2005 to 2016) averages at 19.5 percent due
to the use of the GHGRP data while the earlier portion of the time series applies the default of 10
percent.

Comment: The 10 Percent Oxidation Factor

3)	Appropriate oxidation factor if only one factor is used for all waste disposed between 1990 and 2004.

The existing Subpart HH treatment of methane oxidation requires knowledge of landfill attributes to
calculate methane flux and assess the corresponding methane oxidation value based on the bin approach.
The bin approach is a conservative estimate based on 800 field estimates of oxidation for a range of
methane flux results, as provided in the SWICS addendum and RTI memo. It is our view that EPA
should use the flux based oxidation factor, as it could be applied more broadly than the current application
in Subpart HH and is the most defensible approach.

Response: EPA appreciates commenter's input on the oxidation factor as applied to estimating
emissions from MSW landfills in Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2016. As stated in the Planned Improvement section of Section 7.1 of the Inventory,
EPA is continuing to investigate options to adjust the oxidation factor from the 10 percent currently
used for 1990 to 2004 to another value or approach such as the binned approach used in the
GHGRP (e.g., 10 percent, 25 percent, or 35 percent based on methane flux). The oxidation factor
currently applied in the later portion of the time series (2005 to 2016) averages at 19.5 percent due
to the use of the GHGRP data while the earlier portion of the time series applies the default of 10
percent.

Comment: The 10 Percent Oxidation Factor

21

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4) Methane leakage from cracks and fissures in the cover, and whether to apply a leakage factor for
landfills when assigning oxidation rates.

We find it very hard to understand how the Agency could know or even estimate the extent of cracks and
fissures at landfills on a site-specific basis or more broadly on a nationwide, inventory basis.

Furthermore, there is no proven or accepted method to determine leakage from cracks and fissures. The
reason is that the flux through the cover (and the fraction oxidized) is dependent upon the interactions
among many factors, including soil and physical properties of cover such as gas porosity; organic content
and moisture; microbiological factors such as temperature and substrate availability; and the presence or
absence of a gas collection system. In a 2011 paper in Environmental Science & Technology, researchers
looked at the surface air methane 13C value at 20 landfills and found that the oxidation percentage was
36%, as compared to an oxidation rate of 37% measured in surface chambers. Based on this result,
methane emitted via cracks and fissures did not appear to be a significant factor, and the presence of
cracks and fissures did not necessarily result in higher emissions or lower oxidation.

The landfill sector does not support the development of additional leakage factors for landfills because
leakage is already reflected in the calculated flux rates. The higher the flux rate the lower the oxidation
rate. We think it is neither valid, nor reasonable to develop leakage factors beyond the GHGRP flux rate
calculations for determining an appropriate methane oxidation rate, without extensive scientific support.

Response: EPA appreciates commenter's lack of support for developing an additional leakage
factor when assigning oxidation rates as applied to estimating emissions from MSW landfills in
Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016. As stated in
the Planned Improvement section of Section 7.1 of the Inventory, EPA is continuing to investigate
options to adjust the oxidation factor from the 10 percent currently used for 1990 to 2004 to
another value or approach such as the binned approach used in the GHGRP (e.g., 10 percent, 25
percent, or 35 percent based on methane flux). The oxidation factor currently applied in the later
portion of the time series (2005 to 2016) averages at 19.5 percent due to the use of the GHGRP data
while the earlier portion of the time series applies the default of 10 percent.

Comment: Data Change for Material Discarded

On page 7-12, Table 7-3 represents Material Discarded. These numbers should add up to 100%. They do
for 1990, but not for any of the other years. These amounts are off significantly enough that it is unlikely
due to rounding.

• 1990-adds to 100%

• 2005 - totals 98%

• 2010-totals 93.8%

• 2011-totals 112.2%

• 2012-totals 91.3%

• 2013-totals 92.7%

• 2014-totals 93.6%

Also, it seems to me that this table should follow Table 4 of EPA's Advancing Sustainable Materials
Management: Facts and Figures 2014 which represents materials landfilled. Rather, it states that it also
includes discards that went to WTE facilities. That being said, the 1990 column matches EPA's SMM
Table 4.

Response: EPA appreciates the commenter's detailed review of the tables in the landfills section of
Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016. EPA has

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reviewed and revised the numbers in and footnotes to the table titled "Materials Discarded in the
Municipal Waste Stream by Waste Type from 1990 to 2014" based on these comments.

Comment: Additional Information for Text

Page 3, Line 22: Another factor is the relatively low price being paid for natural gas

Response: EPA acknowledges that the fluctuation in natural gas pricing may be a factor in the
feasibility of LFGTE projects and will investigate this and other potential factors that are
impacting the development of new LFGTE projects for inclusion in a future Inventory report, as
appropriate.

Comment: Scale-up Factor Needs Clarification

Page 5, Line 27: With respect to the scale-up factor, this is a challenging issue. See the Appendix of the
attached article by Powell et al where they try to address the same issue. They provide an estimate of
MSW in landfills not obligated to report.

The method used by EPA is a little hard to follow. One factor that I want to be sure to consider is that the
landfills not captured in various databases are likely smaller landfills. As such, scaling should be done on
the basis of MSW buried and not on the basis of an estimate of the number of missing landfills. I also
think it important to recognize that the estimates are not likely to be within 12.5% anyway so I do not
think that too much significance should be placed on the factor actually used. Using 12.5% as opposed to
10 or 12 implies more significance than is appropriate.

Response: EPA appreciates the commenter's input and the article reference provided (Powell, J., et
al., 2015, "Estimates of Solid Waste Disposal Rates and Reduction Targets for Landfill Gas
Emissions," Nature Climate Change, 21 September 2015). EPA will review the article and evaluate
the potential to make adjustments to the inventory methodology.

Please refer to the supporting memo "Methodological refinements as applied in the 1990-2016
estimates of U.S. greenhouse gas emissions from MSW landfills to account for emissions from
facilities not reporting to the Greenhouse Gas Reporting Program" from Kate Bronstein and
Meaghan McGrath of RTI International to Rachel Schmeltz of EPA/CCD, April 4, 2018 for more
detail on the steps taken to refine the scale-up factor including use of the Waste Business Journal
database as one of the sources for this work. EPA agrees that landfills not captured in the
databases are likely small and EPA has pursued the path of basing our scale-up factor on WIP,
rather than numbers of landfills not reporting to the GHGRP.

Comment: Discussion with Flare Vendors Suggested

Page 8 - lines 7-18: In evaluating appropriate destruction efficiencies for flares, I encourage EPA to
discuss with some flare vendors as they may have unpublished data that is useful. The values in AP-42
are so old that there should be an opportunity for additional data to be considered.

Response: EPA appreciates commenter's input. EPA acknowledges that the AP-42 document
references is old and potentially outdated. EPA will investigate revisions to the destruction
efficiencies for flares in a future Inventory report, as appropriate.

Comment: Methane Oxidation

If using one value for all landfills from 1990-2004,1 think 10% is biased low. Some of these landfills had
good collection and control, however, I do not have a good basis for suggesting what the oxidation factor
should be. One compromise might be to allow 20% for landfills with gas collection.

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I do not suggest the application of a leakage factor to account for cracks and fissures. While
mechanistically appropriate, there is so much uncertainty in the leakage factor as well as the methane
oxidation rate that adding another factor with a highly uncertain value does not improve estimates of
methane oxidation.

Response: EPA appreciates commenter's lack of support for developing an additional leakage
factor for the oxidation factor as applied to estimating emissions from MSW landfills in Chapter 7
of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2016. As stated in the Planned
Improvement section of Section 7.1 of the Inventory, EPA is continuing to investigate options to
adjust the oxidation factor from the 10 percent currently used for 1990 to 2004 to another value or
approach such as the binned approached used in the GHGRP (e.g., 10 percent, 25 percent, 35
percent based on methane flux). The oxidation factor currently applied in the later portion of the
time series (2005 to 2016) averages at 19.5 percent due to the use of the GHGRP data while the
earlier portion of the time series applies the default of 10 percent.

Comment: Use of LMOP database

I think that considerable caution is needed. The LMOP database is self-reported with no quality control.
In addition, it is not updated when a gas to energy project changes.

Response: EPA appreciates commenter's input. Please refer to the supporting memo
"Methodological refinements as applied in the 1990-2016 estimates of U.S. greenhouse gas
emissions from MSW landfills to account for emissions from facilities not reporting to the
Greenhouse Gas Reporting Program" from Kate Bronstein and Meaghan McGrath of RTI
International to Rachel Schmeltz of EPA/CCD, April 4, 2018 for more detail on the steps taken to
refine the scale-up factor including use of the LMOP database as one of the sources for this work.

LMOP is a voluntary partnership program designed to help reduce methane emissions from
landfills by encouraging the recovery and use of landfill gas (LFG) energy as an energy resource.
To support its mission, LMOP collects information from its Partners (using its approved ICR, No.
1849.07; OMB Control Number 2060-0446) on their landfill gas energy project development
activities as well as basic physical and operational data about municipal solid waste landfills.

LMOP has processes and procedures in place to ensure the data collected is consistent and
accurate.

For example, LMOP provides instructions to Partners on how to collect and report data to EPA.
Once data is submitted, program staff and federal contractor staff review and discuss. Any data
inconsistencies or other issues identified are resolved through follow-up correspondence with the
Partner company representative to obtain needed corrections or clarifications. Data that has been
reviewed and verified is then entered into the LMOP Landfill and LFG Energy Project Database
(LMOP Database). In addition to Partner reported data, LMOP compiles data from additional
publicly available sources such as news articles, press releases, reports, presentations, and
organization websites; state websites, databases, reports, and permits; and EPA's Greenhouse Gas
Reporting Program. For these data sources, LMOP follows the same review processes as outlined
above to ensure data is consistent and accurate.

Comment: DOC

Without question, the DOC of waste entering landfills has changed since 1990 and continues to change as
more fiber is recycled and the residual MSW is enriched in food waste as well as non-recyclables. I
would like to see the DOC vary annually or perhaps in 5 year increments to recognize that the DOC is
changing. More broadly, EPA has estimates of the methane yield for individual waste components and
estimates of waste composition. I would prefer to use these data to calculate L0 and DOC. The L0 based

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on AP-42 results in an empirical value that gives the best curve fit. However, this value, while referred to
as the methane production potential, in fact has lots of other factors embedded given the empirical nature
of the LandGEM model for which it is used.

Comment: Annex Table A-2

I have done extensive analysis of decay rates in consideration of landfill gas collection efficiencies. I
have attached 2 manuscripts that suggest that higher decay rates and lower values of Lo may be more
appropriate.

Response: EPA will review the manuscripts provided (Wang, X. et al. 2015 "Characterization of
Uncertainty in Estimation of Methane Collection from Select U.S. Landfills," Env. Sci. and
Technol., 49, p. 1545-1551 and Wang, X., et al. 2013"Using Observed Data to Improve Estimated
Methane Collection from Select U.S. Landfills," Env. Sci. and Technol., 47, p. 3251-3257) and
evaluate the potential to make adjustments to the inventory methodology for future inventory
reports.

Comment: MCF and open dumps

I would assume that all open dumps in the U.S. were deep. This is because our populations are so high. I
think of shallow open dumps as applicable to rural areas in underdeveloped countries.

Response: For the Final Inventory report, the EPA will revise the text to revise the word "dump"
to match the specific solid waste disposal sites (SWDS) category included in the IPCC 2006
Guidelines and modeled. While there are categories for unmanaged shallow (MCF of 0.4) and deep
(MCF of 0.8) SWDS in the waste model, the EPA does not apportion any percentage of waste being
disposed in these categories at any point since 1940. From 1940 to 1979, a portion of the waste
disposed is assigned to the uncategorized SWDS category (with an MCF of 0.6). The EPA has not
found sources documenting the depth of the unmanaged sites across the US, and therefore models
waste disposed in the IPCC's uncategorized SWDS category.

Comment: Additional Source Attached

I have also attached some work we did for EPA in support of the WARM Model.

Response: EPA will review the work done in support of the WARM model (Levis, J. and Barlaz,
M., 2014, "Landfill Gas Monte Carlo Model Documentation") and will evaluate the potential to
make adjustments to the inventory methodology section for future inventory reports.

7.2 Wastewater Treatment

Comment: Suggestion for Methodology of Characterizing Production of Pulp and Paper Sector
NCASI has previously submitted comments on some of the parameters used by the agency (see
Supporting Material), and offers the following input.

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Production. EPA continues to characterize production of the pulp and paper sector as the sum of
woodpulp production plus paper and paperboard production, based on data from the Food and Agriculture
Organization of the United Nations (FAO). As NCASI has commented in prior years, summing wood
pulp, paper, and paperboard production results in double counting, because the majority of wood pulp
production is used to produce paper and paperboard at integrated mills (an integrated mill includes both
pulping and papermaking at the same facility, with a single wastewater treatment system). Therefore,
production statistics used by EPA to represent the pulp and paper sector are too high, resulting in
exaggerated estimates of pulp and paper industrial wastewater methane emissions.

As we have suggested before, a more appropriate method for characterizing total pulp and paper sector
production would be to sum paper production, paperboard production, and market pulp production. The
American Forest and Paper Association (AF&PA) publishes this information annually in its Statistical
Summary reports, which are submitted each year to the US Library of Congress, and which EPA has cited
as a source of information used to update industry wastewater generation rates.

Response: EPA thanks the commenter for their input on the accuracy of estimating emissions from
industrial wastewater treatment in Chapter 7 of the Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2016. EPA is in continued discussions with NCASI to evaluate the availability of
more accurate data for use in revising the factors used to estimate emissions from wastewater
treatment at pulp and paper manufacturing facilities.

Comment: Average Outflow

EPA characterizes wastewater generation per ton of production based on water discharge statistics from
AF&PA Sustainability Reports. These are the most current and relevant data for this characterization,
and NCASI submits no comments on this use other than to emphasize that the agency should ensure it is
using the most current version of the AF&PA Sustainability Report.

Comment: Organic Loading in the Outflow

EPA characterizes the organic load in untreated wastewater using a legacy value of 0.4 gram BOD per
liter of untreated effluent and a multiplier of 2 to convert from BOD to COD. NCASI has very limited
data on untreated effluent organic load. Therefore, until additional data are available, we cannot suggest
an alternative value.

Comment: Production Statistics for Pulp and Paper Sector are Inaccurate
On page A-9, lines 2-5 of Annex 3.14 to the draft inventory, EPA outlines how pulp and paper
industry production data used to estimate the sector's industrial landfill methane emissions are derived
(by summing wood pulp, paper, and paperboard production data from FAO). As indicated above, this
approach results in double counting because the majority of wood pulp production is used to produce
paper and paperboard at integrated mills. Therefore, production statistics used by EPA to represent the

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pulp and paper sector are too high, resulting in exaggerated estimates of pulp and paper industrial landfill
methane emissions.

In summary, the agency's use of FAO statistics overstates the pulp and paper industrial sector's
production by double counting pulp used to produce paper and board at integrated mills, which in turn
results in estimates of pulp and paper sector industrial wastewater treatment and industrial landfill
methane emissions being far too high. The agency should use production data from AF&PA's Statistical
Summary reports to avoid this double counting. This will result in more accurate characterization of
industrial wastewater treatment and industrial landfill methane emissions from this sector.

Annex 3: Methodological Descriptions for
Additional Source or Sink Categories

Annex 3.14 Methodology for Estimating CH4 Emissions from Landfills

Comment: Additional Information Attached

Annex Table A-2: I have done extensive analysis of decay rates in consideration of landfill gas collection
efficiencies. I have attached 2 manuscripts that suggest that higher decay rates and lower values of L0
may be more appropriate.

Response: EPA will review the manuscripts provided (Wang, X. et al. 2015 "Characterization of
Uncertainty in Estimation of Methane Collection from Select U.S. Landfills," Env. Sci. and
Technol., 49, p. 1545-1551 and Wang, X., et al. 2013 "Using Observed Data to Improve Estimated
Methane Collection from Select U.S. Landfills," Env. Sci. and Technol., 47, p. 3251-3257) and
evaluate the potential to make adjustments to the inventory methodology for future inventory
reports.

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Appendix A: List of Reviewers and Commenters

EPA distributed the expert review chapters of the draft Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2016 to a list of 177 expert reviewers across all sectors of the Inventory. The list below
includes names of those expert reviewers who submitted comments as part of the Expert Review
Period.

•	Hendrick G. van Oss - U.S. Geological Survey

•	Kerry Kelly - Waste Management, Republic Services, National Waste & Recycling Association,
Solid Waste Association of North America, SCS Engineers, and Weaver Consulting Group

•	Anne Germain - National Waste & Recycling Association

•	Morton Barlaz - NC State University - Department of Civil, Construction, and Environmental
Engineering

•	David H. Lax - American Petroleum Institute

•	Pamela Lacey - American Gas Association

•	Brad Upton - National Council for Air and Stream Improvement, Inc.

•	Linda S. Heath - USDA Forest Service

•	Stephen Prisley - National Council for Air and Stream Improvement, Inc.

•	Morton Barlaz - NC State University - Department of Civil, Construction, and Environmental
Engineering

Note: Names of commenters are listed in no particular order.

28

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Appendix B: Dates of review

•	Energy, Industrial Processes and Product Use (IPPU), and Waste: October 16 - November 14,
2017

•	Supplemental Energy (Mobile Sources, CH4, N20 updates): October 31 - November 14, 2017

•	Agriculture: October 19 - November 17, 2017

•	Land Use, Land Use Change and Forestry (LULUCF): October 20 - November 17, 2017

29

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Appendix C: EPA Charge Questions to Expert
Reviewers

To facilitate expert review and indicate where input would be helpful, the EPA included charge
questions for the Expert Review Period of the draft Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2016 report. EPA also noted to expert reviewers that while these charge questions were
designed to assist in conducting a more targeted expert review, comments outside of the charge
questions were also welcome. Included below is a list of the charge questions by Inventory chapter.

Energy

General Questions

1. Please provide your overall impressions of the clarity and transparency of the Energy chapter.

2. Please provide any recommendations that EPA can consider to improve the completeness
and/or accuracy of the Energy chapter.

C02from Fossil Fuel Combustion

1. Please provide your overall impressions of the clarity of the discussion on trends in C02
emissions from fossil fuel combustion. Please provide recommendations for any information
that could be added to the discussion to provide additional transparency and clarity.

2. Data for energy use in U.S. Territories comes from the International Energy Statistics provided
by the Energy Information Administration (EIA). At the time of this 1990-2016 expert review
draft Inventory, this source has data only through 2014, the data for years 2015 and 2016 are
proxies in the Inventory. Are there other sources of U.S. Territory energy use that could be
used?

3. Facility-level combustion emissions data from EPA's Greenhouse Gas Reporting Program
(GHGRP) are currently used to help describe the changes in the industrial sector energy use. Are
there other ways in which the GHGRP data could be used to help better characterize the
industrial sector's energy use? Are there ways the industrial sector's emissions could be better
classified by industrial economic activity type?

4. Electricity data is allocated between economic sectors based on electricity sales data provided
by the industry through EIA reports. The data for electricity used in transportation only includes
electricity used for railroads and railways. As a planned improvement, we will look into the
possibility of breaking out electricity used to charge electric vehicles and report that electricity
use under the transportation sector. Are data available on electricity used for battery electric
and plug-in hybrid electric vehicle charging that could be used for this analysis?

5. Are you aware of any newer/updated carbon content coefficients, emission factors, or research
we should be considering?

CH4 and N20 from Stationary Combustion

1. The CH4 and N20 emission factors for electric power sector are based on a Tier 2 methodology,
whereas all other sectors utilize a Tier 1 methodology. The emission factors are primarily taken
from the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Are there other more
U.S. specific CH4 and N20 emission factor data sources that could be utilized?

2. In the 1990-2016 expert review draft Inventory, EPA adjusted the CH4 and N20 emission factors
for combined cycle natural gas units in the electric power sector to use EPA's Compilation of Air

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Pollutant Emission Factors, AP-42, instead of the emission factors presented in the 2006 IPCC
Guidelines. Are you aware of CH4 and N20 emission factors that have been developed more
recently than the AP-42 factors that are as comprehensive (if not more)?

Carbon Emitted from Non-Energy Uses of Fossil Fuels

Please provide your overall impressions of the clarity of the discussion on Carbon Emitted from Non-
Energy Uses of Fossil Fuels. Please provide recommendations for any information that could be added
to the discussion to provide additional transparency and clarity especially in regards to links with the
IPPU chapter.

Mobile Sources

1. Please provide your overall impressions of the clarity and transparency of the proposed mobile
source updates.

2. Please provide any recommendations that EPA can consider to improve the completeness
and/or accuracy of the proposed mobile source updates.

Methodological Updates in Response to Changes to FHWA's Gasoline Consumption Estimation Models

Underlying data sources

As discussed EPA currently uses EIA data to represent total gasoline use and FHWA data to represent
"Transportation" Sector gasoline use. The difference between the two is allocated to the "Commercial"
and "Industrial" sectors for the Inventory. Primarily EPA used the FHWA Table MF-21 to determine
overall Highway gasoline use but there are other sources available including FHWA Table MF-27 as well
as FHWA Table VM-1 (which is used to determine fuel use by vehicle type).

1. Why are there differences in the different sources? Is FHWA Table MF-21 the best source of
Highway gasoline use?

2. Why are there historic differences in FWHA Table MF-21 and MF-27 data? For the most recent
years the MF-21 and MF-27 data match up, except for 2014, will the MF-21 data for 2014 be
updated?

3. Are there other data sources we should be considering?

Proposed update:

The proposed update plans to adjust the gasoline consumption for the lawn & garden and recreational
vehicle non-road categories. However, as shown in the tables above there were also changes to the
other non-road categories in Table MF-24 in 2015.

1. Should the proposed update include adjustments to other non-road categories in table MF-24
(e.g., industrial and commercial)? If so, how should adjustments be made (e.g., use of EPA's
NONROAD model data)?

2. How far back should the backcasting go? Should data back to 1990 be updated or only back to
the previous FHWA of-road update?

3. Are there other approaches to backcast changes in gasoline use that EPA should consider (e.g.,
simple ratios)?

Other changes:

Currently "Transportation" sector gasoline use includes highway and recreational boat categories.

1. Is this an appropriate representation of "Transportation" sector? Should other categories be
included here (e.g., recreational vehicles)?

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Historically, CH4 and N20 emissions from non-road sources have been based on data from EPA's
NONROAD model for different categories of non-road sources. These totals did not always match the
totals from the FHWA MF-24 categories used in the C02 calculations.

2. Should these estimates be made more consistent? If so how? What are the main differences
between the FWHA non-road calculations and EPA NONROAD model results?

3. Generally, are there other updates or changes we should consider for allocation of gasoline use
to different source categories?

Industrial Processes and Product Use (IPPU)

General

1. Please provide your overall impressions of the transparency of the IPPU chapter.

2. Please provide any recommendations of improvements that EPA can consider to improve the
completeness and/or accuracy of the IPPU chapter.

3. For the source categories included in the expert review draft, is the state of the industry current
and accurately described? Are there technologies, practices, or trends that EPA should consider?

Source Specific

1. With the inclusion of a new IPPU source category, EPA requests feedback on the overall chapter
text, assumptions and information on the state of the industry for the following category:

a. Caprolactam, Glyoxal and Glyoxylic Acid Production

2. Please provide input on:

a. Data sources and industry information on production of calcium carbide.

b. Data on carbonate use in non-metallurgical magnesium production.

c. Data on carbonate use in the production of ceramics.

d. Recent/alternative production statistics for various N20 product use subcategories listed
within the Nitrous Oxide from Product Uses source chapter.

3. The EPA seeks comments on assumptions applied to determine the split between primary and
secondary zinc production based on U.S. Geological Survey national totals. Are other
options/data sources available to distinguish between process production totals?

Agriculture

General

1. Provide your overall impressions of the clarity and transparency of the Agriculture chapter.

2. Provide any recommendations that EPA can consider to improve the completeness and/or
accuracy of the Agriculture chapter.

3. Provide feedback on the methodologies and activity data used to estimate emissions for
categories within the Agriculture chapter.

4. Some categories in the Agriculture chapter have used surrogate methods to extend the
emissions time series that are different from the methods used to estimate emissions during the
earlier portion of the time series. These include Enteric Fermentation, Manure Management,
Rice Cultivation, Agricultural Soil Management and Field Burning of Agricultural Residues. Please
provide your input on the surrogate methods used to extend the time series for these
categories.

Source Specific

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1.	For the Manure Management source category, is the state of the industry current and
accurately described? Are there other technologies, practices, trends that we should consider?
Especially:

a.	Are the regional waste management system data used in the inventory (from USDA data
sources) representative of actual observed waste management systems throughout the
country?

b.	Are the trends observed in the inventory waste management system data over time
representative of the trends observed in the industry?

2.	The Manure Management source category relies on national/regional livestock production and
management data for calculating emissions estimates. Are there other data sources that EPA
should be aware of and consider in the calculating these emissions? Especially for:

a.	Waste management system data

b.	Maximum methane producing capacity

c.	Volatile solids and nitrogen excretion rates

d.	Measured emission estimates (by waste management system) to help refine estimates
of methane conversion factors

3.	For the Enteric Fermentation source category, is the state of the industry current and accurately
described? Are there other technologies, practices, trends that we should consider?

4.	The Enteric Fermentation source category relies on national/regional livestock production, diet
and management data for calculating emissions estimates. Are there other data sources or
methods that EPA should be aware of and consider in the calculating these emissions? Especially
for:

a.	Dry matter/gross energy intake

b.	Annual data for the DE, Ym, and crude protein values of specific diet and feed
components for foraging and feedlot animals

c.	Monthly beef births and beef cow lactation rates

d.	Weights and weight gains for beef and dairy cattle

e.	Given the challenges in characterizing dairy diets, are there better methodologies we
could be using to estimate DE for dairy? If so, what would you recommend, and what
sources should be used?

5.	Are you aware of other datasets or products that could be used to inform the management
activities influencing soil N20 emissions for Cropland or Grassland?

6.	Are there management activities that would have a significant impact on soil N20 emissions and
are not currently addressed in the analysis for Cropland and Grassland?

Land Use, Land-Use Change, and Forestry (LULUCF)

General

1.	Provide your overall impressions of the clarity and transparency of the LULUCF chapter.

2.	Provide any recommendations that EPA can consider to improve the completeness and/or
accuracy of the LULUCF chapter.

3.	Provide feedback on the methodologies and activity data used to estimate emissions for
categories within the LULUCF chapter.

4.	As noted in the Introductory section above, some categories in the LULUCF chapter have used
surrogate methods to extend the emissions time series and are different from the methods used
to estimate emissions during the earlier portion of the time series. Please provide your input on
the surrogate methods used to extend the time series for these categories.

33

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Source Specific

1.	Are you aware of other datasets or products that could be used to inform the Land
Representation analysis?

2.	Are you aware of other datasets or products that could be used to inform our understanding of
the current and past management activities for Cropland, Grassland or Settlements?

3.	Are there other management activities that would have a significant impact on carbon stock
change estimates for soils and are not currently addressed in the analysis for Cropland,
Grassland or Settlements?

4.	For the Yard Trimmings and Food Scraps category, is the state of the industry current and
accurately described? Are there other technologies, practices, trends that we should consider?

5.	For the Yard Trimmings and Food Scraps category, are there other data sources that EPA should
be aware of and consider in the calculating these emissions? Especially for:

a.	C storage, decay rates, etc. for yard trimmings and food scraps

b.	Decay rates of food scraps, leaves, grass, and branches

c.	National yard waste compositions

d.	Precipitation range percentages for populations for the decay rate sensitivity analysis

6.	For the Peatlands Remaining Peatlands category, is the state of the industry current and
accurately described? Are there other technologies, practices, trends that we should consider?
Especially:

a. We estimate a rapid decrease of peat production from 2010-2012, with a flattening out
of the decrease after 2012. Is this in line with industry trends?

7.	For the Peatlands Remaining Peatlands category, are there other data sources that EPA should
be aware of and consider in the calculating these emissions? Especially for:

a.	Peat production (mainly Alaska, which has not had reported peat production since 2012
due to a lack of survey responses from industry)

b.	Data to help us develop U.S.-specific emission factors—we currently use IPCC default
emission factors.

Waste

General

1.	Please provide your overall impressions of the clarity and transparency of the Waste chapter.

2.	Please provide any recommendations that EPA can consider to improve the completeness
and/or accuracy of the Waste chapter.

Wastewater

1.	The wastewater source category relies on national production data from a variety of sources for
calculating emissions estimates. Are there other data sources that EPA should be aware of and
consider in the emissions calculations of this source?

2.	Please provide input on any additional sources of wastewater outflow or BOD production that
we may not consider in our industrial methane emissions calculations. Do our estimates of the
percent of wastewater treated anaerobically seem reasonable?

3.	For domestic wastewater emissions, please provide input on:

a.	Any additional sources for the N content of sludge, amount of sludge produced, and
sludge disposal practices.

b.	The estimates of the percent of BOD removed by aerobic, anaerobic, and other
treatment systems for our methane estimates.

34

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c. The protein estimates and overall calculations for nitrous oxide. For example, do you
have suggestions for developing a country-specific factor, rather than the IPCC default
factor, to estimate the amount of nitrogen from industrial and commercial sources co-
treated with domestic wastewater?

4. Are there additional industries that are sources of methane or nitrous oxide emissions that
should be included in the wastewater inventory? Are there available sources of national-level
data for these industries?

5. Do you have suggestions for improving the discussion of our methodology? Is there any
additional information that should be included to provide additional transparency?

6. Is the state of domestic and industrial wastewater treatment current and accurately described?

Landfills

Scale-Up Factor for MSW Landfills

A scale-up factor is applied in the inventory to account for landfills that do not report to the GHGRP
Subpart HH (MSW landfills). We calculated a scale-up factor of 12.5% percent for the 1990-2015
Inventory based on the percent difference between the 1990-2014 Inventory emissions and the GHGRP
emissions as reported for 2010-2015 and back-casted GHGRP emissions for 2005 to 2009. The GHGRP
emissions from 2010-2015 were used to back-cast emissions for 2005 to 2009 using a linear Excel
forecasting function. In the 1990-2015 Inventory, we applied the 12.5% scale-up factor to the back-
casted emissions for 2005 to 2009, and the directly reported GHGRP emissions for 2010 to 2015. We
applied the same 12.5% scale-up factor for the draft 1990-2016 Inventory for 2005 to 2016, and are
working to refine the scale-up factor for the final 1990-2016 Inventory.

The steps we have taken to date to calculate a more precise scale-up factor include developing a list of
facilities that do not report to the GHGRP by extracting GHGRP MSW landfills from the LMOP 2017
database and the Waste Business Journal (WBJ) 2016 database. This list currently includes more than
1,600 landfills. However, we are not confident that this list does not include C&D landfills or industrial
waste landfills due to the lack of details in the LMOP or WBJ databases. Without expert insights, we
believe a desk-top search would be required to identify any C&D landfills or industrial waste landfills
that should be removed from this list.

Additionally, we are working on several manual QA/QC steps, with help from stakeholders, to confirm
that no landfills in the list of non-reporting facilities can be matched to any GHGRP landfills. Matching
the GHGRP facilities to those in the WBJ and LMOP databases is challenging due to the variety of names
for a given landfill and the differences in GPS coordinates across the databases.

We are currently considering two options for a scale-up factor that are based on either:

a) The percentage difference in total waste-in-place between the non-reporting facilities
and the GHGRP MSW landfill facilities, or

b) The percentage difference in net methane emissions between the non-reporting
facilities and the GHGRP MSW landfill facilities.

While we have not completed a full QA/QC review of the list of non-reporting landfills, we are
presenting two values for options (a) and (b).

a) Option (a) yields a scale-up factor of approximately 11%. See Table 1, orange cell. This value
was determined from the estimated total waste-in-place for non-reporting facilities compared

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to facilities reporting to the GHGRP. Available waste acceptance data from LMOP and WBJ was
used to determine waste-in-place for the non-reporting facilities. To calculate GHG emissions
for non-reporting facilities, 11% of the total GHGRP emissions for each year of the time series
would be applied. Note that this value is based on a pre-QA/QC review of the non-reporting
landfills database. A QA/QC review is currently underway.

Table 1. Scale-up Factor based on total waste-in-place (WlP)for 2015

Calcs.2 (non-adjusted)

WIP (MT)

Comments

Non-reporting facilities
(2015)

1,604,238,495

Does not exclude any C&D or inerts to be
consistent with GHGRP total WIP.

GHGRP (RY2015)

12,936,398,280

Total WIP for reporting landfills (RY2015)

Total

14,540,636,775

100

b) Option (b) yields a scale-up factor of approximately 26%. See Table 2, orange cell. This value
was determined from estimated methane emissions for the non-reporting landfills. We used
the Inventory Waste Model (first order decay methodology) and estimated annual waste
disposal data that excludes an average amount of C&D and inert waste (23% of C&D and inert
waste excluded per facility; same disposal amount included in the model for each year of
operation) and the same default factors as applied in previous Inventories for DOC, MCF, etc.
and a 10 percent oxidation factor. To calculate GHG emissions for non-reporting facilities, 26%
of the total GHGRP emissions for each year of the time series would be applied. Note that this
value is based on a pre-QA/QC review of the non-reporting landfills database. A QA/QC review
is currently underway.

Table 2. Scale-up Factor based on Net Emissions, as calculated with adjusted WIPfor 2015

Calcs.3 (adjusted for
C&D/inerts)

Net Emissions
(MMT)

Comments

1990-2015 Inventory

4.63

—

Total as calculated by the Waste Model using
the back-casted GHGRP data and 12.5% scale-
up factor for 2005-2016. Included for
reference.

Non-reporting facilities
(2015)

1.27

Excludes the GHGRP average of C&D/inert
waste of 23% for each non-reporting facility.

GHGRP (RY2015)

3.64

Total as reported to the GHGRP in RY2015.
Data obtained from FLIGHT in C02e.

Total

4.91

100

Scale-Up Factor Questions:

1) Please comment on additional datasets that we can use to generate and/or refine a list of non-
reporting landfills. Datasets with WIP data and start/closure years are needed to develop a
scale-up factor for landfills that do not report to the GHGRP.

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2) How should we consider landfills that "off-ramp" from the GHGRP going forward with respect to
the scale-up factor? For context, only facilities that generate 25,000 MT C02e annually are
required to report to the GHGRP. A facility can off-ramp (i.e., stop reporting) to the GHGRP if it
meets one of the following criteria:

a. Emissions < 15,000 MT C02e for 3 consecutive years

b. Emissions < 25,000 MT C02e for 5 consecutive years

c. Approximately 16 landfills have off-ramped to date. If we consider these landfills as part
of the non-reporting set of landfills, should we adjust the scale-up factor accordingly for
the year(s) after facilities stop reporting?

3) Please comment on the best approach for applying a scale-up factor. We are currently applying
the same scale-up factor for 2005 to 2016. Does it make more sense to apply a scale-up factor
for blocks of time (e.g., 5 years), annually, when GHGRP facilities off-ramp, etc.?

Landfill Methane Oxidation for 1990-2004 in the Inventory Time Series (for MSW Landfills)

For the period of 1990-2004 in the Inventory time series, a national estimate of methane generation and
emissions are calculated using a combination of secondary data sources that detail the annual quantity
of waste landfilled and the annual quantity of methane recovered from facilities with landfill gas
collection and control systems. A 10% oxidation factor is applied to all facilities for the years 1990 to
2004.

We are considering revisions to the value of the oxidation factor and possibly using two oxidation
factors, one for waste disposed at facilities with landfill gas collection and control systems, and the other
without. We currently do not have a way of assigning a percentage of waste disposed in landfills with
gas collection or without for those years. Given that this is a national inventory and we do not have
facility-specific data for all landfills in the U.S., we need data sources that discuss trends in the
installation of landfill gas collection systems, including when the system became operational and at
which facilities. The data available for 1990-2004 is currently national level waste generation; it is not
landfill-specific.

Oxidation Questions:

1) Please comment on available data sources to address trends in the installation of landfill
gas collection systems.

2) Please comment on appropriate oxidation factors for these two general categories (with
and without landfill gas collection systems).

3) Please comment on an appropriate oxidation factor if we were to use one oxidation
factor for all waste disposed at landfills between 1990 and 2004.

4) Please comment on methane leakage (e.g., from cracks and fissures in the cover) with
respect to oxidation factors. If we apply a higher oxidation factor, say 20%, should we
also apply a leakage factor to waste disposed at landfills with gas collection and control,
or all landfills in general?

Disposal Factor for Industrial Waste Landfills

Industrial waste is estimated for two sectors, pulp & paper and food & beverage. We apply a default
disposal factor to estimated annual production data for both sectors.

For pulp & paper, we assume a disposal factor of 5% of the annual amount of woodpulp and paper and
paperboard produced per year. The same 5% disposal factor is applied annually across the time series
(1990-2016) for pulp & paper.

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For food & beverage, we apply a factor that considers the amount of waste landfilled from an EPA study
in 1985 (EPA 1993, as referenced in the Waste chapter) and the annual amount produced in a given year
in the time series. The production data is based on the following: red meat carcass weight, poultry
carcass weight, vegetables processed (apples, citrus fruit, other non-citrus fruit, and grapes). The
disposal factor varies by year because it incorporates the annual production for that year.

Disposal Factor Questions:

1)	Please comment on the pulp & paper disposal factor and whether we should use a disposal
factor based on the GHGRP Subpart TT data.

2)	Please comment on new studies that include data on food processing to landfill disposal ratios
or annual quantities landf illed.

38

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