<&EPA
United States
Environmental Protection
Agency
Summary of Public Review Comments and Responses:
Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2018
May 2020
U.S. Environmental Protection Agency
Office of Atmospheric Programs
Washington, D.C.
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Responses to Comments Received during the Public Review Period on
the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2018
Preface 3
Commenter: American Fuel and Petrochemical Manufacturers (AFPM) 4
Commenter: American Gas Association 6
Commenter: American Petroleum Institute (API) 7
Commenter: Colorado State University 11
Commenter: Environmental Defense Fund, Clean Air Task Force, 12
Apogee Economics and Policy, and The Wilderness Society 12
Commenter: National Association of Clean Water Agencies (NACWA) 14
Commenter: National Cattlemen's Beef Association 15
Commenter: National Lime Association 17
Commenter: National Waste & Recycling Association, SCS Engineers, Solid Waste Association of North
America, Republic Services, Waste Managment, Weaver Consulting Group 18
Commenter: POET, LLC 25
Commenter: Private Citizen 27
Commenter: Private Citizen 28
Commenter: Private Citizen 29
Commenter: University of Michigan 30
Commenter: Water Environment Federation 31
Other Comments 31
Commenter: Anonymous 31
Commenter: Anonymous 32
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EPA thanks all commenters for their interest and feedback on the annual Inventory of U.S. Greenhouse
Gas Emissions and Sinks. Per Federal Register Notice 2020-02139 published on February 12, 2020, EPA
announced document availability and request for comments on the draft "Inventory of U.S. Greenhouse
Gas Emissions and Sinks: 1990-2018" report. The EPA requested recommendations for improving the
overall quality of the inventory report to be finalized in April 2020 and submitted to the United Nations
Framework Convention on Climate Change (UNFCCC), as well as subsequent inventory reports.
During the 30-day public comment period which ended March 13, 2020, EPA received 17 sets of
comments, including 34 unique comments in response to the notice. This document provides EPA's
responses to technical comments on methods and data used in developing the annual greenhouse gas
inventory. The verbatim text of each comment extracted from the original comment letters is included
in this document, organized by commenter. Full comments can be found in the public docket here:
https://www.regulations.gov/docket?D=EPA-HQ-QAR-2019-0706. EPA's responses to comments are
provided immediately following each comment excerpt.
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iiter: Amerl * i •/, - ii>. n-* *1 *,i>. i <<:turers (AFPM)
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0009
David Friedman
Comment 1: Re: Percent of C02 from refining that results from flaring
This comment is in respect to the Energy chapter of the report, specifically on the section describing
GHGs from the refining sector. On page 3-68, the report states, "Almost all (about 98 percent) of the C02
from refining is from flaring."1 Based on previous reports issued by EPA, AFPM believes that this
statement is inaccurate and contradicts determinations made in these previous reports.
In both the 20152 and 20193 Industrial Profile reports, EPA includes charts that summarize petroleum
refinery sector GHG emissions by source (see Appendix below). The refinery GHG emissions by source
include: Combustion of Fuel, (percentage share of 63 and 73 respectively), Catalytic Cracking/Reforming
(approx. 23%), Flaring (approx. 2.5%), and other sources (such as Hydrogen Plant, Sulfur Removal Plant,
etc.). The sum of the published 2015 and 2019 percentage shares of Combustion of Fuel, Catalytic
Cracking/Reforming, and sources other than flaring total more than 97 percent.
As written, the 2020 report implies that the numbers are now transposed and that flaring now accounts
for 98 percent of a refinery's GHG emissions. The calculations in the 2015 and 2019 reports are also
more consistent with the refining industry's own determinations on the contribution of flaring to the
overall GHG emissions in a refinery.
AFPM recommends that EPA reevaluate the refinery GHG summary and apply from the earlier reports
the determination that flaring contributes a very small portion (less than 2.5%) to a refinery's overall
GHG emissions.
1 Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2018, 3-68.
2 Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Petroleum Refining
Industry. (2010). Retrieved 10 March 2020, from https://www.epa.gov/sites/production/files/2015-
12/documents/refineries.pdf.
3 Greenhouse Gas Reporting Program Industrial Profile: Petroleum Refineries Sector (2019). Retrieved 10 March
2020, from https://www.epa.gov/sites/production/files/2019-
10/documents/petroleum_refineries_industrial_profile_9_25_2019.pdf.
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APPENDIX
2015 Industrial Report
Figure 2. Contribution of different emission sources to tbe nationwide C02 equivalent GHG emissions from
petroleum refineries.
E
2019 Industrial Report
FIGURE 1: 2017 PETROLEUM REFINERIES SECTOR: EMISSIONS BY
SOURCE3 b
Flares
2.4%
Sulfur Recovery Units
1.5%
Other
0.5%
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Response: The Inventory text in Section 3.6 on Petroleum Systems has been edited to clarify that the
emissions discussed in this section are fugitives (leaks, venting, and flaring), not combustion sources.
See pp. 3-68 to 3-70 in Section 3.6 of the report.
iter: Ameri - m > Association
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0010
Pamela Lacey
Comment 2: Re: Emission estimates for Natural Gas Systems
The GHGI directly affects AGA and its members because it provides the best available estimate of
national average GHG emissions from our members' operations - including natural gas local
distribution, transmission, and storage. In addition, the GHGI also provides the best available
estimate of the national average methane intensity of the product our members deliver to
customers, measured from wellhead to the customer. As demonstrated by previous Inventories, the
methane intensity of delivered natural gas in the U.S. already falls well below even the most
stringent thresholds for immediate climate benefits achieved through coal to natural gas switching."
As the 2020 Draft GHGI shows, natural gas emissions from distribution systems have declined by 73
percent from 1990 through 2018, including an almost 1% additional reduction between 2017 and
2018. This emissions reduction has been achieved largely through replacing cast iron and
unprotected steel distribution mains with modern medium and high-density polyethylene (MDPE or
HDPE) or cathodically protected steel pipe and upgrading metering and pressure regulating stations
to replace high bleed pneumatic devices. Increasingly, our members are also seeking additional
opportunities to reduce emissions, for example through their commitments in the EPA Methane
Challenge program to reduce emissions from pipeline blowdowns or to enhance programs for
reducing pipeline dig-ins (third party damage). We look forward to seeing how these emission
reduction efforts can be reflected in future GHGIs.
AGA appreciates EPA's ongoing efforts to improve emission estimates based on new research.
While the 2020 Draft GHGI contains no proposed changes in methodology for estimating emissions
from natural gas distribution, transmission or storage,5 AGA appreciates and supports EPA's
proposals to update emission estimates for upstream and midstream segments of the natural gas
supply chain to incorporate data from recent studies and from reporting under EPA's GHG
Reporting Program (GHGRP). For example, AGA supports the use of updated GHGRP reported data
in the exploration segment well completions with and without reduced emissions completions
(RECs), demonstrating a 72% decrease in exploration emissions from 1990 through 2018 and an
8.3% reduction from 2017 to 2018.6 AGA also supports EPA's use of updated methodology using
GHGRP data and the Zimmerle et al. 2019 study to improve the estimate of emissions from
gathering and boosting compressor stations in the production segment.7
4 See AGA's Analysis of EPA's 2019 GHGI (May 23, 2019) at https://www.aga.org/research/reports/epa-updates-
to-inventory-ghg-may-2019/.
5 See 2020 Draft GHGI at page 3-98.
6 See 2020 Draft GHGI at page 3-83.
7 See 2020 Draft GHGI at pages 3-83 and 3-91.
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Response: EPA appreciates the comment and has noted potential use of data from the Methane
Challenge program in the planned improvements text for Natural Gas Systems. See page 3-101 of the
report.
iter: Ameri * 11 - mi sum Institute (API)
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0012
Karin C. Ritter
Comment 3: Delayed Cokers in Refining
API has advocated the use of GHGRP data for the refining sector (Subpart Y) since all U.S. refineries have
been required to report CH4, C02, and N20 emissions for all major activities starting with emissions that
occurred in the year 2010.
For delayed cokers, an updated calculation method was promulgated by the U.S. EPA in December 2016,
which became mandatory starting with reporting year 2018. The update to the calculation methodology
resulted in higher reported methane emissions from delayed cokers in 2018 compared to previous years
of reporting. API recognizes that the update did not impact all facilities reporting under Subpart Y
equally, since some facilities had adopted the updated methodology earlier.
API concurs with EPA's approach to update the time series estimate for 1990-2018 using a ratio of
reported delayed cokers and GHGRP emissions from 2017 to 2018 in order to ensure continued
consistency of emissions estimated between the GHGI and GHGRP for the refining sector.
Response: EPA appreciates the comment.
Comment 4: Offshore Petroleum and Natural Gas Production
In previous discussions with EPA, API supported the continued use of updated Gulfwide Emission
Inventory (GEI) data to ensure the utilization of the most current representation of activities and
emissions for offshore operations. EPA has implemented this approach in the GHGI by calculating vent
and leak EFs for offshore facilities in GOM federal waters for major complexes and minor complexes
using Bureau of Ocean Energy Management (BOEM) GEI emissions data from the 2005, 2008, 2011, and
2014. EPA acknowledged that this approach addresses only production in the federal waters of the Gulf
of Mexico (GOM). Notably, EPA considered a 4-step process of assigning production type for each
complex. The approach potentially counts the same complex up to four times across the GEI's for 2005,
2008, 2011, and 2014.8 It is unclear as to how the number of complexes counted were reconciled with
the BOEM GEI Inventory and which number of complexes were used in order to achieve the results in
the Draft GHGI 2020 update (Table 3-48 of Draft GHGI). The complex counts and approach should be
reconciled with BOEM and explained as to how the total complex counts were used.
Additionally, BOEM GEI had a step-change in their reporting process which incorporated more minor
sources from 2005 to 2008. EPA should note if that step-change or other main factors were the driver(s)
for the increase in the number of complexes. EPA should further note that the "increase" in C02
emissions between 2005 and 2018 was the result of more comprehensive reporting and changes in
8 U.S.EPA (2019), "Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2018: Updates Under Consideration
for Offshore Production Emissions", September 2019 (Table 4, page 8).
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emission factors. Lastly, it would be beneficial to understand whether EPA's emissions trends over this
period accounted for a 50% reduction in platforms and an 80+% reduction in well starts.
API contends that using source specific emission factors may be preferable to the approach taken by
EPA of defining major and minor 'complexes' along with major or minor 'structures', and assigning
average emissions to each type of complex. This approach is not fully transparent regarding the process
used for assigning the emission sources to the complex categories and calculating the respective
emission factors.
Concurrently, EPA calculated GOM federal waters flaring emissions using flaring volumes reported in Oil
and Gas Operations Reports (OGOR), Part B (OGOR-B). EPA's approach used the EF basis of kg/MMBtu
(with year-specific heat content), applying it to OGOR-B flared gas volumes. The other option was to use
BOEM's GEI emission factors however, according to the EPA, this was not chosen because OGOR-B
flared gas volume data are available each year, versus the GEI data that is available only during
publication years, However, BOEM already collects and assesses emissions based on OGOR-Data. BOEM
completed an in-depth QA/QC of GOADS-2011 data submittals for volumes vented and flared with the
values reported to the Office of Natural Resources Revenue (ONRR) through Oil and Gas Operations
Report (OGOR) forms. Additionally, BOEM contacted operators and reconciled flare/vent estimates.
Given this extensive review, it is appropriate to use BOEM emission factors and not duplicate an existing
effort. Furthermore, BOEM is in the process of developing a new web-based emissions reporting tool.
BOEM anticipates collecting emissions data using the new web-based reporting tool for CY2021 and for
those emissions to be reported annually.
API welcomes EPA's discussion of the fact that the previous Inventory allocated all GOM federal waters
flaring emissions to offshore gas production facilities, which explains the shifting of estimated emissions
between the petroleum and natural gas systems in the GHGI. Moreover, in order to combine its GHGI
and OGOR-B datasets, EPA assumed that the 2011 OGOR values, which indicate that 80% of flared gas is
from oil complexes and 20% of flared gas is from gas complexes, is broadly representative and applied it
to all prior years (1990-2010) that were originally attributed to all gas flaring. This is due to the fact that
separate volumes of gas flared and gas vented were not available prior to 2011 and EPA relied on data
provided by the Minerals Management Service (MMS) Staff from 1990-2008. API contends that it is
appropriate and more representative to allocate flaring to both offshore oil and gas complexes, however
the methodology of percent (%) allocation of flared gas from oil vs gas complexes should be reviewed
versus BOEM and their historical MMS data to assess EPA's selection of the 80%/20% assignment.
API is also noting that new data is becoming publicly available on oil and gas venting and flaring. Clearly
the trend favors flaring (vs. venting) because most gas is now produced at modern deepwater facilities.
A 2017 Bureau of Safety and Environmental Enforcement (BSEE) report9 (Tables 1 and 2) confirms that
oil-well gas is primarily flared (in those instances when not captured and exported to market) and that
nearly all the gas released from floating deep-water structures is flared. Given the much higher GHG
effect of methane (vs. C02), this is a very important distinction and highly favorable trend.
The U.S.EPA included in the current GHGI calculations of production based EFs for offshore facilities in
the Pacific and Alaska regions, using data from the GHGRP. API understands that under 40CFR 98.233
(s)(2)(i), production facilities in GOM State Waters, Pacific and Alaska Regions reporting to the GHGRP
adjust previously calculated emissions using the duration of operations for calendar years that do not
overlap with the most recent GEI. API concurs that the increase in CH4 emission estimates from offshore
oil production are due in part to the inclusion of emissions from facilities located in GOM state waters
9 https://www.bsee.gov/sites/bsee.gov/files/5007aa.pdf
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and the Pacific and Alaska regions. API also notes that the increase in offshore emissions attributable to
oil production is due to the fact that a much higher percentage of offshore facilities in the current
Inventory are classified as oil rather than gas.
API requests further information for the EPA calculated GHGRP production-based emission factors in
non-GEI years. The GHGRP methodology for non-GEI years requires the leaks, flaring, and fugitive
emissions reported to be scaled based solely on operating hours. Subsequent scaling of operating hour
based emissions by production volume might not be representative of actual emissions. Additionally,
API is concerned that the use of production data from all sites in conjunction with emission factors that
are limited to the largest emitting sites (those reporting to the GHGRP) might skew the emission
estimate for the specific region.
API recognizes that the implementation of EPA's updated methodology results in decreases in CH4 and
C02 emissions from natural gas systems, due to the reallocation of venting and flaring emissions
between the Petroleum and Natural Gas segments. Most notably, in previous GHGIs all C02 emissions
from flaring were reported under Natural Gas Systems.
API notes that the major factors affecting the lower CH4 and C02 emissions from offshore production
include:
• Reductions in methane emissions from offshore operations can be directly related to more
stringent limitations imposed by BSEE related to venting and flaring. Venting and flaring is
limited by 30 CFR 250 Subpart K which often required the installation of separate flare and vent
meters (after May 2010) and limits the amount of flaring/venting allowed. In addition, in 2012,
BSEE issued guidance for requesting departure approval to flaring or venting beyond allowable.
No flaring or venting without permission is allowed except in limited circumstances, permitted
on a case-by-case basis at BSEE's discretion. When considering requests to approve flaring or
venting, BSEE does not consider the avoidance of lost revenue to be a justifiable reason.
• Industry as a whole is utilizing more VRU equipment to capture releases and moving away from
venting and toward the safer alternative of flaring which results in overall lower methane
emissions. As a consequence of this important development over the past 10 years less gas is
being vented. Even though oil-well gas production (for which there may be a greater incentive
to flare) now (since 2016) exceeds gas-well gas production, the volume of gas flared or vented
has declined. While total gas production has also declined, total flaring/venting volumes have
remained relatively stable at around 1% of total gas production.
• Removal of older platforms, mainly in shallow water and nearer to shore, and installation of
new, state of the art platforms in deep water much further from shore.
Response: Additional documentation was provided in the memo, "Inventory of U.S. Greenhouse Gas
Emissions and Sinks 1990-2018: Updates for Offshore Production Emissions," clarifying how complex
counts were developed.10 Additional text was provided in the GHG inventory and the memo to clarify
the data sources for complexes. The trends over time are due to the underlying trends in the complex
counts and emissions as reported to BOEM. Emissions estimates were calculated using complex-level
factors for offshore operations in GOM federal waters and using production-based emission factors for
offshore operations in state waters. An estimate of emissions source-level emissions was developed
using the fraction of emissions in each category in the GOM federal waters data set, applied to GOM
federal and state water total emission estimates, and using the fraction of emissions in each category
10 https://www.epa.gov/sites/production/files/2020Q4/documents/2020 ghgi update - offshore production final.pdf
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in GHGRPfor Pacific and Alaska offshore production, and applied to the total estimates for Pacific and
Alaska offshore production. The emission source-level estimates are available in the supplementary
excel annex files for Petroleum and Natural Gas Systems.11
Regarding the use of emission factors calculated from data from the from the GHGRP reporting
population for Pacific and Alaska offshore production, alternative data sources are unavailable.
Regarding the use of the GEI versus OGOR-B data, the emissions estimates were calculated using
OGOR-B. GEI data is currently available for the years 2005, 2008, 2011, 2014, and 2017. The OGOR-B
dataset can be used to calculate flaring emissions for the full 1990 to 2018 time series. EPA applied the
OGOR-B data because it is more readily available across the full time series. EPA is aware the BOEM
GEI studies may be updated more frequently in the future and will assess the data as it becomes
available. Regarding upcoming availability of emissions data for offshore production, this feedback
has been noted in the Planned Improvements section of the GHGI. See pages 3-82 and 3-101 of the
report.
Comment 5: Gathering and Boosting Operations
API supports separating the GHGI emission estimate for G&B from the estimate for onshore production
and natural gas processing. EPA updated the gathering and boosting (G&B) station emission estimation
methodology based on CH4 measurements at G&B stations and from data provided since 2016 under
the GHGRP. EPA applied the national average ratio of compressors per station and the national-level
scaling factor, both based on year 2017 data, from the Zimmerle et al. study and did not re-evaluate the
ratio or scaling factor for other years in the public review draft of the Inventory.
API finds that using GHGRP developed equipment level emission factors for sources not included in the
Zimmerle et al. field study is the best available data at this time. The U.S.EPA approach for scaling
GHGRP emissions to the national level closely matches the Zimmerle et al. approach of scaling the
Production sector data (1.07 compared to 1.075) for 2017. However, API contends that the Zimmerle et
al. approach is the more conservative and preferred approach. The GHGRP Gathering and Boosting
volume of gas received can be reflective of gas transported from one gathering station to another
instead of new production from well sites. For example, the 2017 quantity of gas received for the G&B
segment (44,187,605,033mscf) exceeds the total produced gas volume in Dl desktop
(33,755,773,191mcf based on 2017 Dl Desktop data pulled in June2018).
The Zimmerle et al study found great variability in the compressor counts per station and in the fraction
of produced gas reported under GHGRP to Drilling Info production data at the basin level. API notes that
simplifying the approach would potentially result in a lower appearance of GHGRP coverage and an
increased emission estimate.
API suggested during the expert review phase of the proposed methodology updates that,
• Data quality filters are applied in order to avoid including production data scaling where less
than 6% of the gas is sold and for basins where the reported produced gas is >200% of the
Drilling Info production.
• A sensitivity analysis is performed to document the impact of using a national-level approach vs.
1 1
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alia.
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a basin-level approach to scale up national emissions.
It is not clear that such an analysis or data quality checks were undertaken by EPA and incorporated in
the data that is presented in the public review draft GHGI. EPA should also confirm that for the current
GHGI it applied the most recent GHGRP data (October 2019 GHGRP data release). For example, in the
November 2019 methodology update memo for the dehydrator category does not appear to include
desiccant dehydrators emissions.
Response: Additional text clarifying the development of the scale-up factor and the use of national-
level versus basin-level approaches has been added to the Inventory and the memo, "Inventory of U.S.
Greenhouse Gas Emissions and Sinks 1990-2018: Updates to Natural Gas Gathering & Boosting Station
Emissions."12 In the final Inventory, the most recent GHGRP data were used to calculate emissions, and
an estimate for desiccant dehydrator emissions was added.
arado State University
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0018
Dan Zimmerle
Comment 6: Re: Page 3-91, lines 18-25
I recommend an explicit mention of the 'compressors/station' assumption in our methodology; since the
GHGRP does not report station counts, that factor should be noted, and if possible confirmed & updated
over time.
Response: Additional text was added to the Inventory to document the compressors/station
assumption (see page 3-93) and to note that if data are available, this assumption will be assessed
over time (see page 3-101).
Comment 7: Re: Gathering infrastructure outside of compressor station boundaries may not be
included in the methodology
There is some amount of additional gathering infrastructure that is outside of compressor station
boundaries, but not specifically on well pads. These sources are not included in our study, and it is
uncertain if these sources were estimated in your methodology section. This should be clarified.
Response: Additional text was added to the Inventory make this clarification. See pages 3-93 to 3-95
of the report.
Comment 8: Re: Scaling factor
As in the first comment, the scaling factor (cell C75, sheet 3.6-8) of 1.075 was valid for the 2017 ratio of
GHGRP gas production to Drililnglnfo™ production data, but should be confirmed & updated over time.
Response: Additional text was added to the Inventory to note that the scaling factor will be updated
over time if possible. See page 3-101 of the report.
12 https://www.epa.gov/sites/production/files/2020Q4/documents/2020 ghgi update - gb stations final.pdf
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Comment 9: Re: Statement that the second largest methane source at G&B stations is "compressor
venting and flaring" on page 3-83
If this is reference to our report, it should be "venting and fugitive." Perhaps our abbreviation of F&V
was misunderstood. We counted flaring as a separate category, and that also appears to be consistent
with the annex tables.
Response: The text in the Inventory was corrected based on the information provided by the
commenter (see pages 3-93 to 3-95).
'Mi' I ¦ 11 f! < 'in ,*i ¦ "" I'OnsJr 1 l id ¦ b ' .1 1 rrlh vi ¦ " \
Apogee Economi 11.! i vlhk \ ilderness Socie> ,
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0014
David Lyon, David McCabe, and Laura Zachary
Comment 10: Re: Natural Gas and Petroleum Systems estimates
We are concerned that the draft 2020 GHGI would deepen the Inventory's existing underestimate of
natural gas and petroleum systems methane emissions, exacerbating the existing problem already
present in previous editions of the inventory. While we appreciate EPA's hard work to improve the
Inventory and we recognize the value in research into up-to-date emission factors for equipment used in
the gathering and boosting segment of the natural gas sector, EPA should not move from emission
estimates for the segment based on Marchese et al's site-wide measurements to emissions estimates
based solely on Zimmerle et al's bottom-up surveys. As numerous studies have demonstrated [Alvarez
et al 2018, Brandt et al 2014, and references therein], bottom-up equipment-based inventories
consistently underestimate emissions from natural gas facilities for a variety of reasons.
Furthermore, the appropriateness of site-level measurements as a measure of true facility emissions
was recently validated by Alvarez et al 2018, who compared site-level measurement and basin-wide
measurements for 9 basins, showing excellent agreement for 7 of the 9 basins and agreement within
uncertainty for all basins. In contrast, the disagreement between equipment-based survey approaches
and facility-level emissions measurements has been demonstrated, as mentioned above. As described
by Brandt et al 2014, there are a number of systematic reasons why equipment surveys underestimate
emissions.
The impacts of the proposed changes are substantial. The recalculations to the natural gas system
methods, dominated by changes to the G&B segment, resulted in an average decrease in total natural
gas system methane emission estimates of 14.1 MMT C02 Eq., or 8 percent, across the 1990 through
2017 time series. Annual G&B station methane emission estimates decreased by an average of 36
percent in the current Inventory for the 1990 to 2017 time series, compared to the previous Inventory.
Looking specifically at methane emission estimates for 2017 further illustrates the dramatic decrease
due to the proposed revisions. The combined impact of GHGI 2020 methane emissions revisions across
the natural gas system to 2017, compared to the previous Inventory, is a decrease from 165.5 to 139.1
MMT C02 Eq. (26.5 MMT C02 Eq., or 16 percent). A substantial portion of that change, the revisions to
the G&B segment resulted in a decrease from 55.5 to 32.0 MMT C02 Eq. (23.5 MMT C02 Eq., or 42
percent). Revisions to the G&B segment accounted for 23.5 of the 26.5 MMT C02 Eq. (or 88 percent) of
the total decrease from the natural gas system methane emissions estimates for 2017.
For the reasons described above, EPA should not move forward with the changes to the methodology
for estimating emissions from gathering and boosting outlined in the Draft Inventory.
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Alvarez et al 2018 estimated that U.S. Petroleum and Natural Gas System methane emissions in 2015
were 13±2 million metric tons, approximately 60 percent higher than 2017 EPA Greenhouse Gas
Inventory estimate. The study relied primarily on site-level measurement data to extrapolate emissions,
which were then validated with independent, basin-level top-down estimates. For gathering stations,
Alvarez et al 2018 estimated emissions based on data from Marchese et al 2015, which were based on
around 100 site-level measurements and adjusted upward by around 10 percent to account for
emissions from facilities above the sampled range of the log-normal distribution. EPA's proposed change
to gathering station emissions would widen the discrepancy between Alvarez et al 2018 and the GHGI to
around 80 percent, which is inconsistent with numerous peer-reviewed papers that have determined
basin-level emission estimates are substantially higher than regional estimates derived from GHGI data
or methods.
The main cause of this 80 percent discrepancy likely is large, anomalous emission rates caused by
malfunctions or other abnormal events that are difficult to both quantify with component-level
approaches or categorize within a traditional, source-based emission inventory - even a high-quality
bottom-up inventory such as Zimmerle et al 2019. Therefore, the proposed approach would
inadequately account for super-emitter emissions in the G&B sector and cause EPA's estimate to
deviate further from empirically-based estimates.
We therefore do not support EPA's decision to move away from using empirical, site-level data from
Marchese et al (2015) to estimate methane emissions from gathering and boosting stations. For future
considerations of updates to this source, we suggest that EPA consults the EPF and CATF stakeholder
feedback on the 2018 GHGI memos, describing an alternative method that uses data from both GHGRP
and Marchese et al to most accurately estimate total emissions with a best approximation of source-
specific emissions.
Component emission factors for 2016/2017 should not be used for historic emission years. In the
proposed revisions, EPA uses Zimmerle et al 2019 calculated emission factors for compressors, tanks,
acid gas removal units, combustion slip, dehydrators, yard piping, and separators across all years in the
inventory time series (1990-2018). Above we suggest that EPA should not proceed with using the
updated methodology as discussed in the Draft Inventory. If EPA chooses to nevertheless use this
methodology, given that Zimmerle et al state that the lower nationwide emissions that result from their
component emission factors (based on a 2017 survey), compared to the nationwide results from
Marchese et al, may be in part due to improved technologies and industry practices implemented in the
past few years, what assumptions does EPA make in applying the Zimmerle et al 2019 emission factors
to revise Inventory emission estimates for 1990-2016? On what basis does EPA conclude that Zimmerle
et al emission factors are representative of earlier years?
For the remaining G&B station components (station blowdowns, dehydrator vents, pneumatic devices,
flare stacks, and pneumatic pumps), EPA calculates emission factors for 2016-2018 using year-specific
GHGRP subpart W data. However, for 1990-2015 for those GHGRP-based components, EPA uses 2016
emission factors. Why does EPA believe that GHGRP-based emission factors for 2016 are representative
of earlier years?
Response: In their paper, Zimmerle et al. discussed differences between the Zimmerle et al. study
(current Inventory data source for gathering stations) and the Marchese et al. study (previous
Inventory data source for gathering stations). The differences noted in Zimmerle et al. are: (1) the
Zimmerle et al. study uses an updated and likely more representative mix of stations in terms of
throughput and complexity, (2) the Zimmerle et al. study accessed component level activity and
emissions data from the GHGRP, which were not available at the time of the Marchese et al. study,
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and which represented data from a large set of operators for the entire U.S., (3) the two studies
utilized different measurement methods, and (4) there may have been operational improvements to
G&B stations and/or construction of new lower-emitting stations during the intervening years
between studies due to increased attention to CH4 emissions across the natural gas value chain.
The Zimmerle et al. study detected a number of large emitters. For example, the study noted that"For
most leaker factors, 50% or more of emissions are due to the largest 5% of emitters." The set of
emission factors developed in the Zimmerle et al. study which were used to calculate emissions in the
GHG Inventory include estimates for all emissions detected in the field campaign, including estimates
for large emitters, and the study notes that these "Large emitter emissions have substantial impact on
major equipment emission factors, adding 70% - 83% to the impacted major equipment factors."
EPA considered an approach using the Zimmerle et al. (measurements conducted in 2017) and GHGRP
(data available starting in 2016) data in recent years and using from Marchese et al. (measurements
from 2013 and 2014) in earlier years but did not implement it in the Inventory due to incongruencies
between the studies noted above. If the Marchese et al. study in emissions and activity data were used
for early years of the time series (e.g., 1990-2014) and the Zimmerle et al. and GHGRP data were used
in more recent years (e.g. 2016-2017), there would be a large decrease in emissions over a short
period of time due to this transition. Some fraction of the decrease would likely be attributable to
improvements in technologies and industry practices. However, as noted above there are other
differences between the studies such as study representativeness and the difference between the two
is likely not entirely due to changes in technologies (or any other single factor). For this reason, EPA
did not implement an approach that uses data from both of the studies in different parts of the time
series.
i iter: Nati ' "tiatio.i "i l< m -v k!i \ • mp:i« ¦ iu' \ '
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0016
Cynthia A. Finley, Ph.D.
Comment 11: Re: wastewater treatment emissions from publicly owned treatment works (POTWs)
The wastewater treatment category includes publicly owned treatment works (POTWs), septic systems,
and industrial wastewater treatment systems. NACWA's review focused on emissions from POTWs.
NACWA has submitted comments on the wastewater treatment section since the 2005 Inventory, and
we appreciate the clarifications that EPA has made over the years for the emissions calculations and the
factors that are used in the calculations. Several references were updated in the 2017 Inventory to
better reflect current characteristics of the sector. However, more work needs to be done on updating
data sources. For example, the outdated 2004 Clean Watershed Needs Survey (CWNS) was still used as
the basis for the percent of wastewater flow to aerobic and anaerobic systems, the percent of utilities
that do and do not employ primary treatment, and the wastewater flow to POTWs that have anaerobic
digesters. The forecasts made using the 2004 CWNS and previous editions of the CWNS may not
accurately reflect recent trends and practices for wastewater utilities.
Another factor that should be updated is the wastewater flow of 100 gal/person/day, which was taken
from a 2004 document published by the Great Lakes-Upper Mississippi River Board of State and
Provincial Public Health and Environmental Managers. Due to droughts and effective water conservation
measures, many areas of the US now have wastewater flows significantly less than this value. NACWA
14
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recommends that EPA consider updated wastewater flow references that represent current wastewater
flow in other regions of the country.
NACWA agrees with EPA's planned improvements for the Inventory and encourages development of US-
specific methodologies and emission factors when appropriate. As NACWA has explained in comments
on the Inventory in previous years, the Association believes that the nitrogen loading rates for
N20effluent are sourced incorrectly and that using information from the existing National Pollutant
Discharge Elimination System (NPDES) database will yield more accurate and justifiable loading rates.
The NPDES permitting program represents long-term, nationwide facility performance that would allow
emissions estimate projections over the time series represented in the Inventory. EPA should also
investigate additional references for nitrogen loading rates.
NACWA also asks that EPA consider reformatting the explanations of the variables used to calculate
methane and nitrous oxide emissions. Both the value used in the calculation and the source should be
clearly stated, preferably in bullet or table form. The current paragraph format, which generally does
not include the value used in calculation, increases the difficulty of reproducing the emissions
calculations.
Response: EPA appreciates the commenter's feedback on the emissions estimates for POTW, and the
encouragement to develop U.S.-specific methodologies and emission factors as described in the
Planned Improvements within Section 7.2. Each year in compiling estimates, EPA looks for updated
wastewater activity data sources and we appreciate any future suggestions provided by the
commenter or others on specific data sources for wastewater flow and sources to replace the CWNS.
We are aware of a voluntary survey ofPOTWs that is currently being administered by EPA's Office of
Water that could provide valuable updated activity data depending on response rate and
representativeness of facilities that reply. We ask the commenter to encourage its members to
complete the survey to ensure the resulting data may be used for future Inventories.
EPA has considered the suggestion to estimate nitrogen effluent loads based on data reported under
EPA's National Pollutant Discharge Elimination System (NPDES) Program. Unfortunately, very few
POTWs are required to report their effluent nitrogen concentration or load, and those that do are
typically required to meet more stringent limits than the average POTW. At this time, EPA is unable to
confirm that these data would be representative of the entire industry. In addition, this would
represent a departure from the IPCC accepted methodology and would require substantiation that it
results in a more robust estimation of these nitrous oxide emissions.
EPA also appreciates the formatting suggestion and will explore ways to improve the clarity of the
explanation of the variables in the emission equations and the sources for those variables in future
reports.
>. iter: Natr. ,i *i - ^ i 4 ^ ••ration
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0004
Scott Yager, Mary-Thomas Hart
Comment 12: Global Warming Potential Methodology
The Draft Inventory notes that, in 2018, enteric fermentation emissions from cattle accounted for 1.92%
of all United States GHG emissions. To complete this calculation (in addition to other contribution
15
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percentage calculations in the Draft Inventory), EPA utilized the GWP100 methodology. As EPA seeks to
improve its inventory, NCBA urges the Agency to forgo the GWP100 methodology, instead adopting the
GWP* methodology - specifically with regard to methane emissions. Under the United Nations
Framework Convention on Climate Change (UNFCCC), reporting of GHG emissions has been
standardized in terms of C02-equivalent (C02-e) emissions using Global Warming Potentials (GWP) over
100 years, but the conventional GWP100 methodology does not adequately capture the different
behaviors of long-lived climate pollutants (LLCPs) and short-lived climate pollutants (SLCPs). The
atmospheric lifetime and radiative impacts of different GHGs differ dramatically. Acknowledgement of
this reality led to the widescale adoption of the GWP100 methodology. GWP100 equates emissions
using a scaling factor - C02-e. GHGs are assigned a GHG equivalency, then that number is used to
determine the emissions' potential impact. Following GWP100, a pound of methane equates to 25
pounds of C02. Thus, methane is calculated as 25C02e. However, this simplified scaling factor fails to
recognize the amount of time emissions remain in the atmosphere - an equally important factor in
determining potential atmospheric impact. The GWP* methodology seeks to remedy this oversight.13
Anthropogenic warming estimations are largely determined by the cumulative total emissions of LLCPs
and the emission rates of SLCPs. GWP* equates an increase in the emissions rate of an SLCP with a
single "pulse" emission of C02, and thus considers not only the initial intensity of GHGs, but also the
amount of time that they remain in the atmosphere. This approach is a significant improvement on the
conventional GWP100 methodology. Further, the GWP* methodology modifies the conventional GWP
definition to consider C02 warming equivalents (C02-we) rather than C02-e. Following GWP*, SLCPs can
be incorporated directly into carbon budgets consistent with long-term temperature goals, because
every unit of C02-we emitted generates approximately the same amount of warming, whether it is
emitted as a SLCP or a LLCP. This is not the case for conventionally derived C02-e measurements.
Response: As noted by the commenter, EPA uses 100-year Global Warming Potentials (GWP) from
IPCC Fourth Assessment Report as required in reporting annual inventories to the UNFCCC. This is
required to ensure that national GHG Inventories reported by all nations are comparable. The
Inventory present estimates on a gas by gas basis to allow users to understand relative contribution
across all sources of methane, see Table 2-1. The report also includes unweighted estimates in
kilotons (i.e. in Table 2-2 of the Trends chapter on p. 2-4) and stakeholder/researchers can and have
used these values to apply other metrics. We are also tracking the ongoing work of the IPCC in this
area related to the development of their Sixth Assessment Report. EPA takes note of the supplemental
materials submitted with the comments.
Comment 13: Greater Recognition of Grassland Carbon Sinks
NCBA is pleased with the Agency's effort to recognize existing GHG emission offsets. As the Agency
noted in the Draft Inventory, carbon sinks account for a 20% offset of agricultural GHG emissions -
significantly reducing the net impact of the industry. NCBA encourages the bolstering of this section
generally, so that regulated stakeholders and consumers alike can assess the net impact of GHG
emitters. Going forward, NCBA urges EPA to specifically consider the environmental benefit of managed
grazing, a conservation practice implemented by ranchers across the country. It is well-known that
13 Cain, M., Lynch, J., Allen, M.R. et al., Improved calculation of warming-equivalent emissions for short-lived
climate pollutants, Clim Atmos Sci 2, 29 (2019). https://doi.org/10.1038/s41612-019-0086-4.
16
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rotational grazing leads to increased carbon sequestration.14 Globally, if soil organic carbon in
agricultural lands and grasslands increase 10% over the course of the 21st century, carbon dioxide
concentrations in the atmosphere could be reduced by 110 ppm.15
Response: Improved grazing management such as rotational grazing is an activity that EPA would like
to capture better within the GHG inventory but has proved to be challenging due to lack of a
consistent time-series of national activity data for these alternative grazing management approaches.
EPA would appreciate information on activity data sources that NCBA is aware of so these practices
can be better reflected in the methods currently used to estimate emissions and removals from
livestock management on grasslands.
EPA also notes that the offset percentage or "relative" sink cited by NCBA in their comments is not
presented in the report. We were unable to replicate this value based on estimates in the Inventory
report.
i iter: Natior <, * ciation
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0003
William C. Herz
Comment 14: Re: The IPCC factor used to account for lime kiln dust (LKD) C02 emissions
NLA notes that, as in previous years, the Draft U.S. Inventory of Greenhouse Gases and Sinks 1990 -
2018, published on February 11, 2020, still relies on the inaccurate IPCC factor of 1.02 to account for
lime kiln dust (LKD) C02 emissions, and C02 emissions accounting for off-spec lime and other wastes are
absent.
NLA previously submitted comments in 2013 and 2015 concerning inaccuracies on the U.S. Inventory of
GHG Emissions and Sinks that recommended EPA should discontinue using the IPCC emission factors to
account for LKD emissions, and also take into account C02 emissions from off-spec lime, scrubber
sludge, and other wastes (NLA prior comments are included as an Attachment). This issue is important
to NLA members not only to ensure data accuracy, but to EPA's stated goal of agreement and alignment
with the GHG mandatory reporting system. Currently, EPA calcination emission calculations rely on
output-based emission factors from the relatively outdated IPCC 2006 GHG Guidelines.
NLA's recommendations to adopt accurate calcination emissions calculation methodology for LKD and
off-spec lime, scrubber sludge and other wastes are based not on modelled data but rather on analysis
of actual production data, including accurate measurement of CaO and MgO oxide contents of lime and
LKD provided to NLA from its member companies (see NLA comments 2013). These comments and
supporting data should be sufficient to provide EPA with the basis to generate more accurate emissions
estimates for LKD, off-spec lime and scrubber sludge.
In summary, NLA comments concluded that the IPCC's output-based approach for estimating calcination
emissions from U.S. lime products is highly accurate, but it understates emissions from LKD and other
byproducts/wastes generated in the United States. The NLA recommended that lime calcination
14 Wang, T.; Teague, W.R.; Park, S.C.; Bevers, S. GHG Mitigation Potential of Different Grazing Strategies in the
United States Southern Great Plains. Sustainability, 7 (2015), pp. 13500-13521.
15 Lai, R., Sequestering carbon in soils of agro-ecosystems. Food Policy. 36 (2011), (Suppl. 1): S33-S39.
17
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emissions should be multiplied a factor of 1.06 (not 1.02) to account for LKD, and by 1.02 to account for
wastes generated at lime plants (which are currently not accounted for).
However, in the "Uncertainty and Time-Series Consistency" section of the Draft Inventory, EPA
acknowledges NLA's concern using the erroneous factor to account for LKD emissions. EPA also notes
the sharing of historical emissions data and calculation methodologies between NLA and EPA, but adds
it is still reviewing the information.
EPA also adds other caveats, such as uncertainty regarding the availability of data across time series
needed to generate a representative country-specific LKD factor, and uncertainty associated with the
reliability and completeness of voluntarily reported plant-level production data, and the need for further
research and data to improve understanding of additional calcination emissions to consider revising the
current assumptions that are based on IPCC guidelines.
Further, in the "Planned Improvements" section, EPA cites limited resources and the need for additional
QA for not incorporating NLA's recommendations into the current inventory report.
As previously stated, the NLA conclusions and recommendations were based on accurate NLA member
data. Because EPA continues to use inaccurate IPCC's LKD generation rates, calcination emissions
continue to be understated and we urge EPA to take our recommendations into consideration. Further,
if as indicated, there are other supporting data we can provide that would add weight to our argument,
please let us know.
In addition, we know that EPA has a strong interest in having both the GHG Inventory and the
Mandatory GHG Reporting system be in agreement as much as possible. This is important not only for
EPA's creditability but also for the public's and stakeholders' understanding of these issues as well.
The on-going differences NLA has outlined are significant and should be corrected.
Response: EPA appreciates NLA's comment and interest in improving emissions associated with lime
kiln dust generation (LKD) and has reached out to the commenter to discuss available data and to
advance efforts to address this potential update.
iter: Nati \ aste & Recycling Associate , i '<¦ - 11 gineers,
lid Waste Associate m u 11 »rth Americ 1 publi ,vices, Waste
Managment, Weav> i nsi'luh-
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0005
Jesse Maxwell
Comment 15: Degradable Organic Carbon (DOC)
We are pleased that EPA has evaluated stakeholder input regarding DOC and k values, and is developing
an analysis to update default values for both DOC and k in its Greenhouse Gas Reporting Program
(GHGRP) that then would be applied to the emissions estimates for MSW landfills in the GHG Inventory
data for years 2005 to the present. We previously submitted comments recognizing that the default
DOC value used in the GHGRP does not reflect recent trends in the composition of waste disposed in
MSW landfills. Notably, in 2019, the Environmental Research and Education Foundation (EREF)
published a white paper updating the DOC values for MSW landfills and revised its DOC estimate in 2020
with additional technical data to further substantiate representative DOC values for MSW. We
encourage EPA to account for this recent data in its planned improvements to the GHGRP Subpart HH
18
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methodology to present more accurate emissions data from MSW landfills in the 2005 and later years of
the GHG Inventory. We also offer our expertise in assisting EPA in preparing the anticipated multivariate
analysis that attempts to optimize DOC and k values across our sector.
We also are encouraged by EPA's efforts to identify potential improvements to the DOC and k values for
MSW landfills in the GHG Inventory for years 1990 to 2004. EREF has assembled a comprehensive list of
waste characterization studies, including those evaluated by EPA, for this Inventory time series. EREF
used the reliable data from those studies to reevaluate the DOC values for the years 1990 onward and in
February 2020 provided EPA with its new findings to supplement EREF's 2016 white paper and its
January 2019 updates. The additional data reinforces the need for updating the DOC values and should
be used to inform EPA's process for updating the GHGRP as well as the GHG Inventory.
Chapter 7 of the GHG Inventory explains that EPA uses one DOC value of 0.20 to calculate emissions for
the years 1990 through 2004. The GHGRP allows landfills to use 0.20 for bulk MSW or allows a landfill to
further delineate waste streams by accounting for separate shipments of construction and demolition
(C&D) waste, which uses a DOC of 0.08, and separate shipments of inert wastes, which may use a DOC
of 0.0. If a landfill delineates in this way, it must use a DOC of 0.31 for its MSW volumes, which applies
an artificially high DOC to MSW, and inappropriately overestimates emissions. The required DOC value
of 0.31 fails to account for the significant volumes of C&D and inert wastes that are incorporated in
MSW, and which cannot be separated from the MSW or accounted for distinctly, as can discrete
shipments of inert wastes from industrial or C&D recycling facilities. Please let us know how we can
assist the agency in providing additional data on DOC and k values for this Inventory time series.
As stated previously, in 2016, EREF undertook a state-based study of DOC values for both landfills
receiving only MSW (MSW Only Landfills) and for Non-MSW Material going to MSW Landfills. EREF
updated the 2016 paper in January 2019 and February 2020 with additional information based on new
waste characterization information. The DOC guideline recommended by EPA for MSW Only Landfills is
0.31 and the recommended guideline for bulk material (combined MSW, C&D and inert waste streams)
going to MSW landfills is 0.20. EREF concluded both guidelines over-estimate the amount of organic
waste deposited in landfills, which results in inaccurate estimates of landfill gas generation and methane
emissions. Furthermore, neither of the EPA-recommended DOC values have been reviewed in many
years. It is time EPA update the DOC values for MSW and Bulk waste and we believe that the most
valuable focus would be to reassess the DOC values incorporated in the GHGRP used for inventory years
2005 forward.
EREF reviewed 17 recent waste composition studies for MSW Only Landfills conducted by 13 states and
confirmed that waste composition has, and continues to, change over time, as fewer organic materials
are sent to MSW landfills. Since EPA cites the EREF research as a rationale for reassessing DOC values for
1990-2004, the following quotes from EREF clearly suggest that the data strongly suggest reevaluating
DOC values used in the GHGRP for years 2005 and later:
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 3; 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 DOCMSW values ranging from 0.218 in 1994 to a minimum
of 0.160 in 2015 (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 over time or due to location. The results presented
19
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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.16
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, MSW Landfills
rarely accept MSW exclusively. Rather, most MSW Landfills (landfills in 45 states) are authorized to
accept other Subtitle D wastes in addition to MSW,"17 and often non-MSW materials comprise a
significant percentage of MSW landfills. In addition, EREF notes:
Given that a third of incoming waste to MSW Landfills 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 MSW Landfill waste stream.18
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 MSW
Landfills (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 landf illed waste is 0.167 (Table 7).19
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 0.191 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 8, 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.20
Thus, EREF concludes as follows:
The average computed DOC value for MSW using state data was 0.191, or roughly three-fifths of
the MSW guideline value. The average computed DOC value for bulk waste using state data was
0.167, 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.21
Based on this review of the DOC values for MSW landfills, the waste sector concludes that the long-
standing DOC values developed in the past over-estimate both landfill gas generation and methane
16 The Environmental Research & Education Foundation (2019). Analysis of Waste Streams Entering MSW Landfills:
Estimating DOC Values & the Impact of Non-MSW Materials., pp 8 - 9. Retrieved from www.erefdn.org
17 Ibid., p. 10.
18 Ibid., p. 11.
19 Ibid., p. 13.
20 Ibid., p. 14.
21 Ibid., p. 15.
20
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emissions. The data provided by EREF confirms that two trends are driving the changes in waste
composition at MSW Landfills. First, many MSW landfills are handling less organic matter now, and we
anticipate this trend will continue due to state and local organics diversion goals. Second, the increase of
Subtitle D non-MSW waste disposed of in MSW landfills has altered the DOC for all waste deposited in
MSW Landfills. EPA validates these trends in the GHG Inventory's Chapter 6 discussion of carbon
sequestration of harvested wood products, yard waste and food waste, as Table 6-85 shows a significant
reduction in sequestered carbon since 1990 due to reduced volumes of organic wastes disposed in
landfills.
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 past 20 years. The values now in use
are inaccurate and should not be used going forward. We recommend that EPA review and update the
DOC values for the entire 1990-2018 time series of the GHG Inventory and prioritize updates of the DOC
values used in calculating GHG emissions under Subpart HH of the GHGRP.
Response: EPA appreciates the commenter's feedback on the DOC as applied to estimating methane
generation and emissions from MSW landfills. We also appreciate the information provided about the
most recent Environmental Research and Education Foundation (EREF) white paper. As stated in the
Planned Improvements section of Section 7.1 of the U.S. Greenhouse Gas Inventory of Emissions and
Sinks, EPA is developing a multivariate analysis solving for optimized DOC and k- across the more than
1,100 landfills that report under subpart HH of the GHGRP. This analysis uses publicly available data
directly reported to the GHGRP. The results of this analysis could inform updates to the default DOC
and k-values used by landfills subject to reporting under subpart HH of the GHGRP in calculating their
facility-level emissions. For updates to the DOC to be reflected in the Inventory, the updates also need
to be incorporated in Subpart HH of the GHGRP given its direct use in estimating national-level
emissions from MSW landfills.
Comment 16: The Scale-Up Factor for MSW Landfills
We find the explanation of the methodology EPA employed to arrive at the scale-up factor to be clear.
We also are encouraged that EPA intends to periodically assess and revise the scale-up factor based on
reasonable expectations that landfills that do not report under the GHGRP are likely to be smaller,
closed sites with declining GHG emissions and that reporting landfills will continue to represent a larger
proportion of waste-in-place. For example, starting in 2010, every year fewer landfills have reported
more than the 25,000 MTC02e. Yet, every year, more landfills are included in the GHGRP. This means
that more of the waste is covered by reporting facilities on an annual basis.
Year # of landfills reporting # of landfills >25k MTC02e Total MTC02e reported
2010
1235
975
101,920,033
2011
1240
965
93,830,839
2012
1252
961
94,375,699
2013
1278
946
91,159,615
2014
1290
941
90,817,217
2015
1294
935
89,746,871
2016
1300
914
86,905,137
2017
1304
898
86,464,158
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2018
1313
896
89,215,401
Again, most landfills that are exempt from the GHGRP requirements are old, small, closed landfills. The
potential methane emissions from these sites decrease year over year by approximately 3 percent, on
average. Therefore, the emissions contribution from these sites will continue to decrease compared to
the sites that report via the GHGRP. The scaling factor must be adjusted to reflect the declining
contribution of the exempt sites.
Response: EPA appreciates the commenter's feedback on the clarity of the methodology used to
develop the scale-up factor to account for landfills that do not report to the GHGRP. EPA also agrees
with the commenter's feedback that the scale-up factor should be evaluated on a routine basis. There
is a large amount of uncertainty associated with the number of non-reporting landfills and their total
waste-in-place and the scale-up factor is our best estimate given the available information. EPA plans
to reexamine the scale-up factor for the 1990-2019 Inventory cycle to determine if there are additional
landfills reporting to the GHGRP such that the waste-in-place a mounts for those landfills can be
removed from the scale-up factor assumptions. At the same time, EPA will also account for those
landfills that have stopped reporting to the program because they were able to exercise the off-ramp.
Any additional information from commenters on landfills that do not report to the GHGRP that could
help refine the scale-up factor assumptions are always welcome and appreciated.
Comment 17: Methane Oxidation Factor
Our previous years' comments on the methane oxidation factor used for the 1990 to 2004 Inventory
time series remain unchanged and are repeated below. EPA calculates a national estimate of methane
generation and emissions 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. This 10 percent default factor contrasts significantly with the average methane oxidation factor of
19.5 percent applied through use of GHGRP data, to the later years of the time series (2005 to 2018).
Importantly, the 19.5 percent average oxidation rate incorporated in the GHGRP, subpart HH, emissions
data is premised on a more detailed and up-to-date estimation approach than is the default value of 10
percent. It is also a conservative average value, as the GHGRP methodology restricted the maximum
oxidation rate to 35 percent.
In its work to review and revise the method for calculating methane oxidation under subpart HH of the
GHGRP, EPA acknowledged the need to update the default 10 percent oxidation value. The default value
was based on only one field study, at a landfill without gas collection and control, and did not reflect the
much higher oxidation values found in numerous subsequent, peer-reviewed field studies. Given the
plethora of scientific studies showing methane oxidation to be several times higher than the EPA and
IPCC default value,22 we strongly recommend EPA apply a revised value (perhaps the average oxidation
value from the GHGRP) to the earlier years of the time series.
Response: EPA appreciates the commenter's feedback on the oxidation factor as applied to estimating
emissions from MSW landfills. EPA regularly reviews new literature related to landfill methane
oxidation and investigated 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) or the average oxidation factor across
22 Solid Waste Industry for Climate Solutions, 2.2 Methane Oxidation Addendum 2012, November 19, 2012.
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facilities reporting to the GHGRP (approximately 19.5 percent). At this time EPA has decided not to
revise the methane oxidation factor for the 1990-2004 time series since such a change will likely result
in a noticeable discontinuity in the emissions between 2004 and 2005-2010 (i.e., a jump in emissions
between 2004 and 2005) that would need to be investigated and resolved to ensure methodological
consistency over the time series and to accurately reflect trends. We continue to advance efforts to
improve the methane generation calculations in the landfills section of the Waste Chapter by focusing
on improvements to the DOC and k-value per responses to other comments submitted by this
commenter, in order to make best use of the available resources across the Inventory compilation
process.
Comment 18: The k Factor (Methane Generation Rate Constant)
As discussed above, we are encouraged that EPA is evaluating stakeholder input on k value for both the
1990 to 2004 Inventory series and for 2005 to the present. We also are pleased that EPA is investigating
k values for different climate types against new data and other landfill gas models, as well as assessing
the uncertainty factor applied to these k values in the Waste Model, and we offer our support to EPA in
collecting and evaluating this information. As noted in previous years' submissions, the waste sector is
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.23
The waste 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 rely on these data. For this reason, we support EPA's plan to review and
resolve the significant problems in the k value data set. However, we also suggest that the agency
review L0 value. Although an independent variable, L0 should be considered in conjunction with k value
modifications because it is related to fitting the curve, where the results will be dependent on the
assumptions used for the LO/DOC.
Response: EPA appreciates the commenter's feedback on the k-value as applied to estimating
methane generation and emissions from MSW landfills. As stated in the Planned Improvements
section of Section 7.1 of the U.S. Greenhouse Gas Inventory of Emissions and Sinks, EPA is developing a
multivariate analysis solving for optimized DOC and k-values across the more than 1,100 landfills that
report under subpart HH of the GHGRP. This analysis uses publicly available data directly reported to
the GHGRP. The results of this analysis could inform updates to the default DOC and k-values used by
landfills subject to reporting under Subpart HH of the GHGRP in calculating their facility level
emissions. As the commenter already acknowledged for updating DOC, in order for updates to the k-
value to be reflected in the Inventory, the updates also need to be incorporated in Subpart HH of the
GHGRP given its direct use in estimating national-level emissions from MSW landfills.
23 U.S. EPA, Draft AP 42.2.4: Municipal Solid Waste Landfills, October 2008, p. 2.4-6.
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Comment 19: Compost Emission Factor
Our previous years' comments on compost emission factor remain unchanged and are repeated below.
In ideal conditions, the composting process occurs at a moisture content of between 50 and 60%, but
the moisture content of feedstocks received at composting sites varies and can range from 20% to 80%.
It is common for moisture to be added to dry feedstocks prior to the start of composting to optimize the
biological process. In the calculation of emissions from composting in the draft chapter, it appears that
all incoming wastes were assumed to have a moisture content of 60%. If 60% is not reflective of the
actual weighted average of all feedstocks, this will introduce errors in the inventory calculation that
could be significant.
We recommend that the calculations be based on waste subcategories (i.e., leaves, grass and garden
debris, food waste) and category-specific moisture contents, or ask that further information is provided
on the rationale for assuming 60% as the average moisture content of all inbound materials.
Response: EPA notes the commenteds feedback on the moisture content levels used in the calculation
of emissions from composting. The calculations for composting are based on IPCC Tier 1 methodology
defaults. Under this methodology, the emission factors for CH4 and N20 assume a moisture content of
60% in the wet waste. (IPCC 2006) EPA has included this detail to the Methodology section of Section
7.3 of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2018, as was done in the
previous year's inventory report, so that the source of the moisture content is more transparent. In
addition, EPA continues to include in the Planned Improvements section of Section 7.3 that EPA is
looking into the possibility of incorporating more specific waste subcategories and category-specific
moisture contents into the emissions estimates for composting in the United Stated to improve
accuracy. However, to date the EPA has not been able to locate substantial information on the
composition of waste at U.S. composting facilities to do so. As additional data becomes available on
the composition of waste at these facilities, EPA will consider using this information to create a more
detailed calculation of U.S. composting emissions.
Comment 20: Chapter 6: Land Use, Land-Use Change, and Forestry - Carbon Stocks
In Chapter 6: Land Use, Land-Use Change, and Forestry of the GHG Inventory, carbon stocks from yard
trimming and food scrap in landfills are discussed starting on page 6-128. The carbon stocks are
calculated according to Equation 1 on page 6-131. However, Equation 1 reduces the persistent carbon
by the carbon content twice, effectively reducing the carbon storage value. The formula calculates C
stock (LFC), which is the incoming weight (W) reduced by moisture content (MC), reduced by initial
carbon content (ICC), reduced by degradation of the non-persistent carbon. The formula reduces stored
carbon by the initial carbon content within the braces even though it had previously been accounted for.
Rather the formula shown, it should be:
LFC = W x (1-MC) x ICC x {CS + (1-CS) x e k(t n»}
Additionally, Table 6-87 shows that the decay rates for grass, leaves, branches and food scraps were
0.323, 0.185, 0.016, and 0.156, respectively. Last year's report shows the values on Table 6-81 as 0.313,
0.179, 0.015, and 0.151, respectively. It appears that the decay value for each material increased from
the values shown in last year's report without any explanation. The discussion on the values references
using the 2000 U.S. Census for the latest year's calculation, but the 2010 U.S. Census for the previous
year's calculation. It is unclear why EPA would use the earlier census data instead of the most recent.
We recommend that EPA elaborate on the changed decay rates.
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The waste sector also has questions regarding Table 6-88, which shows the remaining carbon stock in
landfills. Although grass has the highest decay rate and the highest moisture content, it is shown as
having the highest stock in the landfill of all yard trimmings and food scraps. C stocks should represent
the total carbon stored in landfills minus the amount lost from decomposition. By weight, grass should
be 30 percent of yard waste, but because it is composed of 70 percent moisture, the weight is reduced
by that amount. Then, only 53 percent is persistent and it has the highest decay rate and the lowest
initial carbon content. Therefore, grass should have the lowest amount of C in the landfill, not the
highest. It is probable that the figures for grass and branches were inadvertently switched. We
recommend that EPA review the values shown in Table 6-88 to determine their accuracy.
Response: EPA thanks SWANA for their review of the Changes in Yard Trimmings and Food Scrap
Carbon Stocks in Landfills section of the Inventory. EPA is still evaluating the suggested changes to
Equation 1 and will add this evaluation to the list of planned improvements for next year's inventory.
EPA agrees with the comments related to Table 6-87 and the Census data and has corrected the table
and text. EPA also agrees with the comments on Table 6-88: the table category labels were
transcribed incorrectly. EPA corrected these category labels.
Commenter: POET, LLC
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0006
Kyle Gilley
Comment 21: Re: Using ethanol as a strategy to reduce GHG emissions from the transportation sector
We are troubled that over 90 percent of the carbon dioxide emissions in 2018 were associated with
fossil fuel combustion, and over 35 percent of total carbon dioxide emissions are associated with the
transportation sector, making the transportation sector the largest carbon emitter in the U.S. economy.
See Draft Report at ES-11, ES-12. Ethanol is a renewable fuel with significant environmental and
economic benefits that is an important, readily-available tool to help combat transportation sector
greenhouse gas ("GHG") emissions.24 Currently, almost all gasoline in the United States contains 10
percent ethanol; however, higher level ethanol blends-such as E15, approved for use in almost all
conventional light-duty vehicles on the road today-provide additional benefits beyond E10, and are
increasingly available at retail stations across the U.S.
Specifically, ethanol-blended fuels provide, at low cost, substantial GHG emissions benefits. Recent life
cycle analyses show that corn starch ethanol reduces GHG emissions by approximately 40% as
compared to petroleum, and additional analyses predict that these reductions may increase to 50% or
more by 2022 with ongoing innovations in corn cultivation and biorefinery practices.25 Cellulosic ethanol
24 As a methodological matter, we support EPA's adherence to the Intergovernmental Panel on Climate Change's
guidance and the United Nations Framework Convention on Climate Change's reporting requirements to exclude
biofuel estimates
25 USDA/ICF Study, "A Life-Cycle Analysis of the Greenhouse Gas Emission From Corn-Based Ethanol," (Sep. 2018)
https://www.usda.gov/oce/climate_change/mitigation_technologies/LCA_of_Corn_Ethanol_2018_ Report.pdf;
Mueller, "Updated Life Cycle Greenhouse Gas Data for Corn Ethanol Production," (Mar. 2016)
http://illinoisrfa.org/wp-content/uploads/2017/06/UIC-OIG-3_16_v2-l.pdf; Michael Wang et al., Argonne
National Labs, "Well-to-Wheels Energy Use and Greenhouse Gas Emissions of Ethanol from Corn, Sugarcane, and
Cellulosic Biomass for U.S. Use," (Dec. 2012) http://iopscience.iop.org/1748-9326/7/4/045905/pdf/1748-
9326_7_4_045905.pdf.
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provides even more substantial GHG benefits, essentially eliminating the greenhouse gas impacts of
liquid fuel.26 Ethanol plays a central role in transportation sector GHG reduction programs, such as in the
California Low Carbon Fuel Standard program, in which ethanol provides over one-third of all GHG
credits.27 Without ethanol, such programs would not be able to achieve GHG reduction targets and
would do so at a higher cost to consumers and regulated parties.
As a methodological matter, POET supports EPA's adherence to the Intergovernmental Panel on Climate
Change's guidance and the United Nations Framework Convention on Climate Change's reporting
requirements to exclude carbon dioxide emissions associated with combustion of biofuels from the
Inventory totals given the biogenic nature of the fuels. See Draft Report at 3-22, n. 21. The Draft Report
indicates "[n]et carbon fluxes from changes in biogenic carbon reservoirs in croplands are accounted for
in the estimates for Land-Use, Land-Use Change, and Forestry (see Chapter 6)." Id. This portion of the
report does not identify any land use changes specifically associated with corn production for ethanol,
and the scientific literature supports that no such relationship exists. In particular, total land acreage
devoted to corn farming has remained constant since the 1930s.28 Remarkable increases in yield have
allowed farmers to meet greater demands for food and fuel using the same amount of land. Specifically,
acres planted in corn have remained at or below 1930s levels while corn production has increased
seven-fold.29 Indeed, according to U.S. Department of Agriculture projections, annual corn production is
anticipated to surpass 15 billion bushels by 2025 with approximately 2 million fewer acres in
production.30 Further, water usage for corn crop irrigation has decreased over time and
fertilizer/pesticide use has plateaued even as corn harvest has increased substantially.31 These modest
and decreasing impacts contrast with the tremendous environmental impacts of petroleum exploration
and refining, and the associated GHG emissions impacts of fossil fuel combustion.32
Moreover, increased use of biofuels can promote environmental and equity objectives through
maximizing co-benefit improvements in local air quality for low income and vulnerable communities
that have been plagued by harmful pollutants. Specifically, vehicle pollution is a key culprit of air quality
issues for communities of color that breathe, on average, 66 percent more air pollution from vehicles
than white residents.33 Combustion of the fossil fuel component of gasoline and diesel results in harmful
particulates and toxic aromatics like benzene and toluene.34 Increased biofuel-blending can mitigate
26 Id.
27 California Air Resources Board, Data Dashboard- Figure 2 Alternative Fuels Volume and Credits, May 15, 2019.
https://www.arb.ca.gov/fuels/lcfs/dashboard/dashboard.htm.
28 Ramboll, The RFS and Ethanol Production: Lack of Proven Impacts to Land and Water at 11 (Aug. 2019),
https://growthenergy.org/wp-content/uploads/2019/09/Ramboll_RFS_Reset_Document_Final_08_18_2019.pdf.
29 Ramboll at 11-13; K. D. Reitsma, et. al., "Does the U.S. cropland data layer provide an accurate benchmark for
land-use change estimates?" AgronomyJournal, 108(1), 266-272 (2016), https://dl.sciencesocieties.org
/publications /aj/pdfs /108/1/266; J. B. Dunn, et. al., "Measured extent of agricultural expansion depends on
analysis technique." Biofuels, Bioprod. Biorefining, 11(2), 247-257 (2017) 10.1002/bbb.l750.
30 Id. at 12.
31 Id. at 32.
32 E. Parish, et. al., "Comparing Scales of Environmental Effects from Gasoline and Ethanol Production,"
Environmental Management (2013) 51:3017-338 https://link.springer.eom/journal/267/51/2.
33 Inequitable Exposure to Air Pollution from Vehicles in the Northeast and Mid-Atlantic, Union of Concerned
Scientists (June 21, 2010), https://www.ucsusa.org/resources/inequitable-exposure-air-pollution-vehicles
34 See e.g., New Studies Show Ethanol Reduces Emissions and Improves Air Quality, URBAN AIR INITIATIVE (Apr. 11,
2018), https://fixourfuel.com/2018/04/ll/new-studies-show-ethanol-reduces-emissions-and-improves-air-
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these emissions. Biofuels' displacement of harmful fuel additives is further illustrated by a recent study
conducted by the University of California Riverside (UCR), which found that greater use of ethanol-
blended fuels can reduce carbon monoxide, ozone, and particulate matter levels relative to the use of
gasoline-only fuels.35 Thus, biofuel-blended fuel is positioned to ease the pollution burdens low income
and vulnerable communities bear, including reducing the toxic constituents in gasoline.
Further, while other means of alternative personal transportation may be relatively expensive or require
extensive infrastructure upgrades, higher biofuel blends can be utilized by nearly all consumers, and can
be offered at a discounted price relative to higher GHG emitting fuels. Higher biofuel blends are a way to
share the economic advantages of a low carbon transportation sector with low income consumers.
In sum, ethanol should be a key tool in the United States' strategy to reduce the GHG emissions
associated with the transportation sector identified in the Draft Report.
Response: EPA thanks the commenter for the information and perspective on ethanol production and
use. As mentioned, biofuel C02 estimates are presented in the Inventory for informational purposes
only, in line with IPCC methodological guidance and UNFCCC reporting obligations (See Section 3.11 of
the Report). Net carbon fluxes from changes in biogenic carbon reservoirs in croplands are reported in
the Land Use, Land-Use Change, and Forestry sector (See Chapter 6). All non-C02 emissions associated
with combustion for biomass energy are included in the Energy sector (See Chapter 3). Furthermore,
the Inventory reports emissions in line with international conventions on country level reporting which
lists emissions by source or category and not by product life cycle or fuel type. The inventory is a
policy-neutral, technical report providing information on current GHG emissions and sinks and trends
prepared per reporting UNFCCC Annex 1 National GHG Reporting Guidelines (see Box ES-1) and as
such, it is not well-suited as a document in which to outline mitigation opportunities and goals.
ter: Private Citizen
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0013
Bridget Chadwick
Comment 22: Re: spelling out carbon instead of using atomic symbol "C"
Spelling out carbon instead of using the atomic symbol "C" will help readers in a search for discussions
about "carbon intensity" and the "carbon content" of fossil fuels consumed.
Response: EPA appreciates the comment on improving the usability and readability of the annual
Inventory report. Some instances of the use of the atomic symbol "C" were modified for this report but
EPA will continue to look for ways to improve readability in future reports.
Comment 23: Re: Using the unit exajoules to describe the carbon content of petroleum products on
page 3-34
For consistency with the discussion of the "carbon content" of fossil fuels and "carbon intensity" of
energy, elsewhere in the Inventory, the units: MMT C02 eq. / QBtu should be used.
quality/; S. Mueller, et. al., The Impact of Higher Ethanol Blend Levels on Vehicle Emissions in 5 Global Cities, UNI.
OF ILLINOIS AT CHICAGO (Nov. 2018), http://www.erc.uic.edu/assets/pdf/UIC5cities_HEALTH_Novl2_ Final.pdf.
35 University of California CE-CERT, Impacts of Aromatics and Ethanol Content on Exhaust Emissions from Gasoline
Direct Injection (GDI) Vehicles (April 2018).
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Response: The reference to exajoules was replaced with QBtu in the final report.
Comment 24: Re: Referring readers to Table A-41 in Annex 2.1 for "more detail on the C Content
Coefficient of different fossil fuels
Table A-42 should be referenced.
Response: The reference was updated for the final report.
Comment 25: Re: The explanation of how C02 emissions are estimated on page 3-32
This explanation should say that the carbon content coefficients are multiplied by the molecular-to-
atomic weight ratio of C02 to carbon i.e. 44/12, as done in the Annexes on page A-465.
Response: The explanation was updated in the Final Report to reference the molecular-to-atomic
weight ratio.
Comment 26: Re: Box 3-5
This box provides a discussion of fossil fuel carbon content "ranging from about 53 MMT C02 Eq./QBtu
for natural gas to upwards of 95 MMT C02/QBtu for coal and petroleum coke". A short description of
the energy/C02 tables, A-ll to A-39, provided in the Annexes with a table of the average C02 emission
factors of fossil fuels consumed in 2018 (coal 95.6; oil products 72.4 and natural gas 52.9
MMTC02/QBtu) would help readers understand the relationship between C02 emissions [MMTC02],
energy consumption [QBtu] and the carbon intensity of the fossil fuel energy consumed
[MMTC02/QBtu].
Response: The text box was modified in the Final Report (box 3-4) to include a reference to Tables A-42
and A-43 in Annex 2.1 for carbon contents of all fuels.
Comment 27: Re: Figure 3-16 on page 3-34
The key driver "energy consumption" should be shown in this figure.
Response: Energy consumption was not added to Figure 3-16 but was included on Figure 2-15 in the
Final Report to be consistent with information provided in Table 2-14.
Comment 28: Re: Table A-44
In this table, total electricity consumption for 2018 should be corrected to 4004 billion kWh as provided
in the reference document, the EIA Monthly Energy Review, November 2019.
Response: The values in Table A-44 are consistent with prior versions of the EIA Monthly Energy
Review but will be reviewed for future reports and incorporate any updates to EIA data.
ter: Private Citizen
EPA Docket ID No.: EPA-HQ-QAR-2019-0706-0015
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Jeff Moeller
Comment 29: Re: Section 7.2 Wastewater Treatment:
The calculation does not appear to include emissions that may occur in wastewater collection systems.
Wastewater collection systems may be a significant source of emissions, but it may also be quite difficult
to estimate these emissions. I'd recommend noting that collection systems may be another source of
emissions and that more work may be needed on this topic in the future.
Response: As stated in the Planned Improvements within section 7.2 of the Inventory report, although
there are insufficient data to capture emissions from collection systems, EPA plans to update emission
factors for centralized aerobic treatment based on the recently published 2019 Refinement to the 2006
Guidelines for National Greenhouse Gas Inventories. The revised emission factors account for
incoming dissolved methane that is formed in the collection system and liberated during aerobic
treatment.
iter: Private Citizen
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0002
OleksandrStubailo
Comment 30: Re: Figures ES-17 on page ES-30 of the Executive Summary
This figure attempts to provide an overview of the key categories of emissions, but combines categories
that have net positive and net negative carbon emissions in one chart.
When I was looking at the chart, I didn't initially see that categories like "Net C02 Emissions from Forest
Land Remaining Forest Land" represented a negative impact on carbon emissions, since they were
displayed in a similar way to categories with positive impact.
I'd propose displaying those categories in some other way, perhaps by making the bar in the chart a
different color - maybe green instead of blue.
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Figure ES-17: 2018 Key Categories (MMT COz Eq.)a
CO2 Emissions from Mobile Combustion: Road
CO2 Emissions from Stationary Combustion - Coal - Electricity Generation
Net CO2 Emissions from Forest Land Remaining Forest Land"
CO2 Ew^lons from Stationary Combustion - Gas - Electricity Generation
CO2 Emissions from Stationary Combustion - Gas - Industrial
Direct N2O Emissions from Agricultural Soil Management
f CO2 Emissions from Stationary Combustion - Oil - Industrial
CO2 Emissions from Stationary Combustion - Gas - Residential
/ CO2 Emissions from Stationary Combustion - Gas - Commercial
CO2 Emissions from Mobile Combustion: Aviation ¦
CH4 Emissions from Enteric Fermentation: Cattle ¦
CH4 Emissions from Natural Gas Systems ¦
CO2 Emissions from Non-Energy Use of Fuels ¦
Emissions from Substitutes for Ozone Depleting Substances ¦
Net CO2 Emissions from Settlements Remaining Settlements15 ¦
Net CO2 Emissions from Land Converted to Forest Landb ¦
CH4 Emissions from Landfills ¦
Net CO2 Emissions from Land Converted to Settlements'3 ¦
CO2 Emissions from Stationary Combustion - Oil - Commercial ¦
CO2 Emissions from Stationary Combustion - Oil - Residential ¦
Net CO2 Emissions from Land Converted to Croplandb |
Fugitive Emissions from Coal Mining ¦
Indirect N2O Emissions from Applied Nitrogen I
CO2 Emissions from Stationary Combustion - Coal - Industrial I
CO2 Emissions from Mobile Combustion: Other I
CO2 Emissions from Iron and Steel Production & Metallurgical Coke Production I
CO2 Emissions from Cement Production I Key Categories as a Portion of
CO2 Emissions from Petroleum Systems I All Emissions
C02 Emissions from Mobile Combustion: Railways I
CH4 Emissions from Petroleum Systems I
Response: Figure ES-17 has been updated to differentiate key categories from the LULUCF sector that
have a net negative emissions. See p. ES-29 of the report.
Commenter: University of Michigan
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0017
Eric Kort, Alan Gorchov Negron
Comment 31: Re: The treatment of emissions from the offshore oil and gas sectors (pg. 3-76 to 3-77
and 3-93 to 3-94)
Regarding the update to activity data (platform counts): This represents a clear and major improvement
over the prior inventory, and addresses both the previous gap in accounting for state water platforms
and temporal trends.
Regarding the new method for calculating emission factors: We suggest further clarifying differences in
both how emission factors are calculated (including the data sources used) and activity data that is used.
Specifically noting (perhaps in a table form) this information for the different regions (Federal and State
waters in Gulf of Mexico, offshore CA, offshore AK) as well as different categories (major/minor) would
be very helpful.
Regarding upcoming relevant data: We have conducted a recent aerial survey of offshore oil and gas
platform emissions, and have future surveys planned. In these studies emissions from offshore facilities
are characterized and evaluation of different inventory estimates and methods will be provided. As this
work appears in the peer-reviewed literature it will provide additional information to assess and
improve reported offshore emissions.
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Response: Additional information on the calculation of emission factors is included in the memo,
"Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2018: Updates for Offshore Production
Emissions."36 The upcoming availability of data relevant to offshore oil and gas emissions was noted in
the Planned Improvements text for Petroleum and Natural Gas Systems. See pages 3-82 and 3-101 of
the report.
ter: Water Environment Federation
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0008
Patrick Dube
Comment 32: Re: References to sewage sludge
In agreement with the EPA's definition of biosolids, "Biosolids are treated sewage sludge",37 WEF
believes the term "treated" should be included when referencing sewage sludge throughout the
document. For reference, this occurs on: Page 5-25, Line 29, Page 5-28, Table 5-18, Page 5-34, Line 4,
Page 5-34, Line 22, Page 5-35, Line 16, Page 5-39, Line 24, Page 5-39, Line 26, Page 5-39, Footnote 20,
Page 5-40, Line 41, Page 5-40, Line 44, Page 5-42, Line 1, Page 5-43, Table 5-20, Page 6-53, Line 15, Page
6-75, Line 22, Page 6-76, Line 25, Page 6-76, Line 28, Page 6-77, Table 6-40, and Page 6-124, Line 39.
Response: The text has been updated to reflect this clarification.
Other Comments
EPA received two additional anonymous technical public comment as part of the public review of the
draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2018. The comments can be found on
the public docket and is copied below.
ter: Anonymous
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0007
Comment 33: Re: Detailed analysis for transportation sector emissions
In Section 2.2 (Emissions by Economic Sector) Table 2-13 and the preceding text provide detail on
transportation-related emissions by various modes with electricity-related emissions distributed to the
transportation sector. It would be useful to add the same type of detail for the analysis without
distribution of electricity-related emissions (i.e., additionally provide the transportation-related detail
that would sum to the transportation sector emissions in Table 2-10).
Response: A more detailed break-down of CO 2 emissions from fossil fuel combustion in the
Transportation sector is provided by fuel type (including electricity) and transportation mode in
Chapter 3 Table 3-13, with additional detail provided in Annex 3.
36 https://www.epa.gov/sites/production/files/2020-Q4/documents/2020 ghgi update -
offshore production final.pdf
37 https://www.epa.gov/biosolids/frequent-questions-about-biosolids
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iter: Anonymous
EPA Docket ID No.: EPA-HQ-OAR-2019-0706-0011
Comment 34: Re: Estimated costs for Greenhouse Gas Sinks by cost/MMT reduced for the various
types of measures available
There should be estimated costs for Greenhouse Gas Sinks by cost/MMT reduced for the various types
of measures available, ranging from additional trees, to electric car conversion, to nuclear power or gas
power plants replacing coal, so that prioritized measures to reduce greenhouse gases can be understood
and implemented at the lowest marginal cost.
As the 2017 report noted, the decrease in total greenhouse gas emissions between 2016 and 2017 was
driven in part by a decrease in C02 emissions from fossil fuel combustion. The decrease in C02 emissions
from fossil fuel combustion was a result of multiple factors, including a continued shift from coal to
natural gas and increased use of renewable energy ithe electric power sectors, and milder weather that
contributed to less overall electricity use. This is shown in ES-4 Inventory of US Greenhouse Gas
Emissions and Sinks: 1990-2017.
It is important, especially where GHG emissions are growing annually, to begin to or accelerate
abatement procedures, including replacement of industrial or chemical processes which produce for
example Carbon Dioxide or high impact hydrocarbons, by prioritizng those cost measures which produce
the most emissions impact reduction per dollar expended.
Moreover, the costs of reducing GHG should be at a minimum the cost of carbon offsets in any carbon
offset trading market.
If the highest 75% of GHG abatement techniques cost $50 per ton, or $75 per ton, then that should be
the cost of any carbon emissions.
The United States could reduce GHG emissions in 2030 by 3.0 to 4.5 gigatons of C02e using tested
approaches and high-potential emerging technologies. These reductions would involve pursuing a wide
array of abatement options with marginal costs less than $50 per ton, with the average net cost to the
economy being far lower if the nation can capture sizable gains from energy efficiency. Achieving these
reductions at the lowest cost to the economy, however, will require strong, coordinated, economy-wide
action that begins in the near future.
Response: The inventory is a policy-neutral, technical report providing information on current GHG
emissions and sinks and trends prepared per reporting UNFCCC Annex 1 National GHG Reporting
Guidelines (see Box ES-1) and as such, it is not well-suited as a document in which to outline mitigation
opportunities and goals. For more information on assessing implications of mitigation measures
please see EPA's technical report titled Global Non-C02 Greenhouse Gas Emission Projections &
Mitigation Potential: 2015-2050 at this link: https://www.epa.gov/global-mitigation-non-co2-
greenhouse-gases. See also the latest global analysis published IPCC Working Group III report here:
https://www.ipcc.ch/report/ar5/wg3//, noting the latest assessment on mitigation is going and
anticipated to be published in 2021.
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