Document ID: EPA-HQ-OAR-2009-0923-0070
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-06-02T04:00Z

Listed below are the requests from EDF received via a phone call
regarding U.S. Inventory of Greenhouse Gas Emissions and Sinks data. 
After each request is the response which is based on publicly available
information.

Request:  He wants to understand the Gas STAR source pie charts that we
put in our presentations - specifically, what are the inventory sources
that make up those pie pieces.

Response:  Consult the Energy Section 3 and Sections 3.4 and 3.5 of the
Annexes in the 2007 U.S. Inventory found at   HYPERLINK
"http://epa.gov/climatechange/emissions/usgginv_archive.html" 
epa.gov/climatechange/emissions/usgginv_archive.html .  The individual
source categories and their methane emissions begin on page A-143 for
natural gas and page A-151 for petroleum in Annex 3.  The Annex more
thoroughly covers the methodology used to arrive at the results in
Section 3.

Request:  He noted that REC reductions are greater than the entire
inventory number for well completions and had a general question about
how we deal with that when removing NGS reductions from the inventory. 
Also wanted to talk generally about our policy for updating the
inventory and why we haven't done that for this source.

Response:  Generally, when estimating emissions from the natural gas
industry in the U.S. GHG Inventory, CH4 emissions are quantified for
each segment of the industry (e.g., production, processing,
transmission, distribution) based on a bottom up assessment of different
emissions sources. Reductions reported by Gas STAR partners are
subtracted at the segment level.  Please see Annex 3.4 in the 2007
Inventory. 

The Inventory is annually subject to a peer review, a public review and
review by an international team of experts.  Based upon issues
identified during these reviews, as well as experience gained in the
Natural Gas STAR program, the U.S. strives to continually improve the
national Inventory.  EPA has undertaken efforts in the past couple of
years to update the underlying activity data used in the inventory for a
number of sources, including well completions and we are evaluating the
appropriateness of incorporating revised data into the National
Inventory.

We have communicated preliminary revised emissions estimates to external
stakeholders to enable a dialogue among all interested parties about the
potential magnitude of emissions from this industry.  We have used many
of these revised emissions estimates as the foundation for the analysis
used to support development of reporting requirements for this industry
under the Mandatory GHG Reporting Rule. We also intend to incorporate
these revised emissions estimates into our next annual inventory
submission to the United Nations Framework Convention on Climate Change.

Presently, REC reductions reported in the Natural Gas STAR body of work
is larger than well completion venting in the inventory on an annual
basis.  Section 3 of the inventory discusses improvements and future
plans for each sector.  For the natural gas industry, the planned
improvements are discussed on page 3-46.  For the petroleum industry,
the planned improvements are discussed on page 3-51.

In a New York Times article published on October 15, 2009, it is
mentioned that the EPA is currently reviewing and revising methane
emissions from U.S. gas wells.  As a result, the EPA found that the
amount emitted by routine operations at gas wells is approximately 12
times larger than the existing estimate of 9 Bcf.  The NYT article can
be found here at   HYPERLINK
"http://www.nytimes.com/2009/10/15/business/energy-environment/15degrees
.html#" 
www.nytimes.com/2009/10/15/business/energy-environment/15degrees.html# .

EPA has included these revised emission numbers in the MRR. 
Specifically, these new numbers are in the TSD, explained in Appendix B
(pages 79 to 85) and used in the TSD on page 9.  On page 82, the new
2007 U.S. emissions from well completion and workover venting is
approximately 120 Bcf.  The TSD can be found here at   HYPERLINK
"http://www.epa.gov/climatechange/emissions/downloads10/Subpart-W_TSD-02
2310.pdf" 
www.epa.gov/climatechange/emissions/downloads10/Subpart-W_TSD-022310.pdf
.

Request:  It looked to him like NGS reductions, which include both oil
and natural gas production operations, are only removed from the natural
gas portion of the inventory - why is this?  If we were to differentiate
the emission reductions associated with the oil sector, what would these
be (sources and volumes)?

Response:  The methodology in Annex 3 of the inventory indicates how
Natural Gas STAR reductions are applied to the natural gas systems
sector.

Natural Gas STAR considers data at the level of the production sector,
rather than further dividing its reporting into natural gas and
petroleum.  At the same time, the inventory considers data at the level
of natural gas systems production & petroleum systems production.  Often
a Natural Gas STAR reduction activity straddles both natural gas systems
and petroleum systems and is therefore inherently an overall production
sector activity.  The Natural Gas STAR production sector reductions are
not further deconstructed and are thus applied to natural gas systems
production sector.  For example, vapor recovery units (VRUs) can be
installed on both condensate (gas) and storage (oil) tanks, but it is
not a Natural Gas STAR reporting requirement to specify which.

Request:  Do we have a number (%) we can provide publicly about the
amount of gas lost from what comes out of the ground versus what gets to
consumers/export?

Response:  This percentage is not a published statistic but can be
roughly calculated from public sources such as the inventory and such as
EIA gas production data.  It is also important to understand numerical
treatment of gas imports and exports, NGL imports and exports, gas
reinjected, gas consumed on site, gas unaccounted for due to intrinsic
metering errors, and distinguishing between methane versus natural gas
data, which all have first order effects on the resulting percentage. 
Any result using this calculation method would not apply to any specific
site given the top-down nature of the calculation.

Request:  Are changes/updates to the national inventory tracked every
year?  In particular, he noticed that there were changes to past year
volumes in the most recent inventory and wondering why those would
change retroactively.

Response:  Yes, for each annual inventory cycle, the entire time series
is considered and updated.  The entire time series of 1990 to the
present reporting year is updated annually because revised activity data
is applied as it is available.  It is not uncommon for EIA or other data
sources to issue revised estimates for years in the recent past, and
such revisions are tracked by the inventory.  Any changes in the data
sources used are be noted in the executive summary and introduction
sections of the inventory.

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