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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.

o Response: Consult the Energy Section 3 and Sections 3.4 and 3.5 of the 

Annexes in the 2007 U.S. Inventory found at 

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.

o 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. 

o 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.
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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 www.nytimes.com/2009/10/15/business/energyenvironment/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 

www.epa.gov/climatechange/emissions/downloads10/Subpart-W_TSD022310.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)?

o 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.
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 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?

o 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 topdown 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.

o 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.