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MEMORANDUM

FROM: Akachi Imegwu, U.S. EPA, Climate Change Division

TO: Docket EPA-HQ-OAR-2011-0147

DATE: August 3, 2012

SUBJECT: Summary of comments on Subpart W of the final Mandatory

Reporting of Greenhouse Gases Rule (40 CFR Part 98) after promulgation that are 

addressed in the final rule action: 2012 Technical Corrections, Clarifying and 

Other Amendments to the Greenhouse Gas Reporting Rule, and Confidentiality 

Determinations for Certain Data Elements of the Fluorinated Gas Source 

Category

1.0 INTRODUCTION

The 2010 final rule for Subpart W of the Greenhouse Gas Reporting Rule (Subpart W) 

was signed by EPA Administrator Lisa Jackson on November 8, 2010 and published in the 

Federal Register on November 30, 2010 (75 FR 74458). The 2010 final rule, which became 

effective on December 31, 2010, included reporting of GHGs from facilities containing 

petroleum and natural gas systems. The rule does not require control of GHGs, rather it only

requires that facilities containing petroleum and natural gas systems with emissions sources 

above certain threshold levels monitor and report emissions and other related data.

Since promulgation of the final rule in November 2010, EPA proposed the “Technical 

Corrections, Clarifying and Other Amendments to Certain Provisions of the Mandatory Greenhouse Gas 

Reporting Rule” on August 4, 2011 (76 FR 47392) and the “Technical Revisions and 

Clarifications to Subpart A, Subpart I, and Subpart W” on September 9, 2011 (76 FR 56010). 

Stakeholders were given the opportunity to comment on these proposed rules. As a result of 

those comments, EPA made technical and editorial revisions to specific provisions in Subpart W

that were finalized on December 23, 2011 (76 FR 80554). In addition, the Administrator has 

identified within Subpart W a number of technical issues that need to be revised and specific 

provisions that need to be clarified. 

The purpose of this memorandum is to summarize specific comments received from 

hotline questions or meetings with affected industry members, and outline the issues being 

addressed by these final amendments. 

2.0 SUMMARY OF COMMENTS ADDRESSED BY FINAL AMENDMENTS 

EPA received questions related to implementation of the December 23, 2011 final rule 

through the EPA Hotline and through meetings with affected industry members. Several 

questions have resulted in amendments to specific provisions in Subpart W in order to provide 

more clarity and to correct errors. The EPA has also held meetings with several trade 

associations representing industries affected by Part 98, and many questions were presented by 

those trade associations that would be resolved through the amendments to Subpart W.
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For a summary of the submitted comments which are being addressed by technical 

revisions to Subpart W, please see the following table, “Summary of Comments Being Resolved 

By Technical Corrections, Clarifying and Other Amendments.” All identifying information from 

the incoming questions has been removed from the table. 

Technical Issue Questions Submitted to EPA Type and 

approximate 

number of 

submittals

Reference 

1. Amend 

Equation W-6 

in 98.233(e)(5) 

by removing a 

factor of 1000 

to leave the 

calculated 

emissions in 

cubic feet 

rather than 

convert it to 

Mcf

Question: This question relates to Subpart W, 

equation W-6 for desiccant dehydrators. 

Based on the units of the equation variables, the 

resulting units for the equation should be Mcf/year 

(thousand cubic feet per year). 

However, the rule states that the resulting units are 

"Es,n = Annual natural gas emissions at standard 

conditions in cubic feet." I.e., cf/year (cubic feet per 

year). 

Please address this error.

At least 1 

individual

Helpdesk 

submission

2. Amend 

98.233(g)(1) to 

voluntarily 

allow 

reporters to 

take more 

than the 

prescribed 

number of 

sample 

measurements 

per sub-basin 

and well type 

by inserting 

the phrase “at 

least” in the 

rule text.

Question: 98.233(g)(1) prescribes a graduated 

number of measurements or calculations per subbasin and well type (horizontal or vertical) 

depending on the total number of completions or 

workovers - with the maximum required 

measurements or calculations prescribed as 5. Would 

it be acceptable for a company to record the data 

necessary for the calculations or take a measurement 

for each completion/workover within a given subbasin well type combination (e.g. have greater than 5 

measurements or calculations). [which would result 

in more accurate reporting of emissions] If so, would 

the data from each event be used in the emissions 

estimation or would the company be required to 

select only the specified number of values for 

emission estimation purposes?

At least 1 

individual

Helpdesk 

submission

3. Revise 

Equation W15 to clarify 

that “Count” 

refers to those 

separators or 

wells that feed 

Question: Equation W-15. This equation does not 

differentiate between high pressure and low pressure 

separators and whether or not a separator feeds 

directly to a storage tank or to an additional 

separator. Do you need to count all separators or 

only those that feed liquids to a tank at atmospheric 

pressure (where gas can flash)?

It seems that Equation W-15 would be more accurate 

if the definition of 'Count' were changed to 'Total 

At least 1 

individual

Helpdesk 

submission
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oil directly to 

storage tanks.

number of separators dumping liquids to storage 

tanks and wells with throughput less than 10 barrels 

per day.' This would prevent over-counting of 

emissions that do not flash from separators feeding 

to other separators.

4. Revise 

Equation W36 to revise 

the definition 

of parameter 

“ρi” to amend 

the density 

value of CH4

to be 0.0192 

kg/ft3

There appears to be an error in the CH4 density 

defined for Equation W-36 in 40 CFR 98 Subpart W 

of the 12/2/11 pre-publication version of the final 

rule. I think it should be 0.0191 kg CH4/ft^3 at 60°F 

and 14.7 psia, while the 12/2/11 version of the rule 

shows 0.0422 kg CH4/ft^3 at 60°F and 14.7 psia. It 

appears that EPA forgot to convert the density from 

units of lb/ft^3 to kg/ft^3. Using the incorrect value 

in the rule misestimates CH4 emissions by 2.2 times 

too high. Do you plan to correct this in the rule? If 

so, when will you do that? If not, may I use the 

correct CH4 density at 60°F and 14.7 psia (0.0191 kg 

CH4/ft^3) instead of the value of 0.0422 kg 

CH4/ft^3 at 60°F and 14.7 psia that is in the 12/2/11 

version of the rule? For background, my CH4, CO2, 

and N2O density calculations are provided below. 

Thanks for your help. 

Ideal gas law: PV = nRT, or PV = (m/MWT) RT 

For CH4: 

(14.7 psia) x (V ft^3) = (m lb/16 lb/lbmole) x (10.73 

psia-ft^3/lbmole-°R) x (60°F+459.67°R) 

m/v = CH4 density = 0.0422 lb/ft^3 = 0.0191 kg/ft^3 

(compared to 0.0422 kg/ft^3 in Equation W-36 of the 

12/2/11 pre-publication version of Subpart W) 

For CO2 and N2O: 

(14.7 psia) x (V ft^3) = (m lb/44 lb/lbmole) x (10.73 

psia-ft^3/lbmole-°R) x (60°F+459.67°R) 

m/v = CO2, N2O density = 0.1160 lb/ft^3 = 0.0526 

kg/ft^3 (compared to 0.0526 kg/ft^3 in Equation W36 of the 12/2/11 pre-publication version of Subpart 

W)

At least 1 

individual

Helpdesk 

Submission

5. Revise 

Equation W39A to replace 

the parameter 

“ECO2” with 

“Ea,CO2”.

Question: [The questioner] was reviewing the GHG 

reporting rules (40 CFR Part 98), and found a few 

minor errors. 

§98.233(z)(2)(iii) definitions for Eq. W-39A and W39B: 

change "ECO2" to "Ea,CO2" {variable in equation 

and definition should match}. 

At least 1 

individual

Helpdesk 

submission

6. Revise 

98.236(c)(9) by 

removing the 

text, “using 

optical gas 

imaging 

instrument 

per 

98.234(a)(refer 

to §98.233(k)), 

Question: The rule is not clear with respect to 

98.234(a)(5) - Does an acoustic leak detection device 

have to be used to detect through-valve leakage or 

are any of the options in 98.234(a)(1-5) acceptable 

for making such determinations?

Response: Acoustic leak detection devices can 

specifically be used for through-valve leakage. 

However, as per the opening paragraph in 98.234(a), 

any methods listed under 98.234(a) can be used to 

determine through-valve leakages.

At least 1 

individual

Helpdesk 

submission
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or acoustic 

leak detections 

of”

7. Revise 

98.236.c15(ii)(

A), by 

removing 

(a)(8) from the 

list of source 

categories

Question: In 98.236.c15.ii.A, EPA added (a)(8) to 

the list of source categories but did not add the 

corresponding Table W-7 with distribution emission 

factors. Why did EPA add distribution to the list and 

not add the table? NMGC asked this question in 

October 24, 2011 comments but we do not see a 

response to this comment in the response to 

comments.

Response: EPA agrees that 98.236 (c)(15)(ii)(A)

should be updated to reflect the correct citations. 

EPA has updated the citation and removed the 

reference to the natural gas distribution table, W-7, 

and industry segment definition (a)(8). 

At least 1 

individual

Helpdesk 

submission

8. Update Table 

W-1A to 

reflect updates 

to Population 

Emission 

Factors 

Question: I am writing to request confirmation of 

the emission factors published in the "Federal 

Register /Vol. 76, No. 247 / Friday, December 23, 

2011 /Rules and Regulations, TABLE A-1A OF 

SUBPART W-DEFAULT WHOLE GAS 

EMISSION FACTORS FOR ONSHORE 

PETROLEUM AND NATURAL GAS 

PRODUCTION, pages 80591 and 80592. 

Specifically, the emission factors published in the 

table for "Eastern US - Population Emission Factors, 

All Components - Gas Service" and "Western US -

Population Emission Factors, All Components - Gas 

Service" for valves, connectors, open-ended lines, 

and pressure relief valves, have increased by almost 

24 times the emission factors published in the 

previous versions of the rule ("Federal Register / 

Vol. 75, No. 229 / Tuesday, November 30, 2010, 

page 74512"). For example: 

TABLE A-1A OF SUBPART W-DEFAULT

WHOLE GAS EMISSION FACTORS FOR 

ONSHORE PETROLEUM AND NATURAL GAS 

PRODUCTION - Western US (scf/hour/component) 

Valves: 

Federal Register, November 30th, 2010 - 0.123 

scf/hr/component 

Federal Register, December 23rd, 2011- 2.90 

scf/hr/component 

Connector: 

Federal Register, November 30th, 2010 - 0.017 

scf/hr/component 

Federal Register, December 23rd, 2011- 0.396 

scf/hr/component 

Open-ended line: 

Federal Register, November 30th, 2010 - 0.032 

scf/hr/component 

Federal Register, December 23rd, 2011- 0.748

At least 1 

individual

Helpdesk 

submission
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scf/hr/component 

Please provide a basis or explanation for this large 

increase in the emission factor. I was not able to 

locate an explanation for this change in the Technical 

Support Documentation or Response to Comments

Response: Thank you for pointing out the issue with 

the emission factors listed in Table W-1A.

3.0 SUMMARY OF ISSUES FROM INTERNAL REVIEW LINKED TO FINAL 

AMENDMENTS

As mentioned above, not all of the corrections and other amendments correspond directly to 

questions that were raised by reporters. The need for some corrections and other amendments 

were identified as a result of internal EPA review. The following is a list of the issues being 

raised from EPA’s review of Subpart W of Part 98. These issues are listed in the final rule “ 

2012 Technical Corrections, Clarifying and Other Amendments to the Greenhouse Gas 

Reporting Rule, and Confidentiality Determinations for Certain Data Elements of the Fluorinated 

Gas Source Category.”

Summary of Issues from Internal Review Being Addressed by Final Amendments

Not all corrections and other amendments correspond directly to questions that were raised by 

reporters. The need for some corrections and other amendments were identified as a result of 

internal EPA review. Below is a summary of the issues that have been raised from the EPA’s 

review of Subpart W of Part 98.

Changes to 98.233

 Amend Equation W-7 by changing the parameter FRp to FR and clarifying that Tp is 

cumulative amount of time in hours for venting.

 Amend Equation W-8 by revising the definition of parameter SPp to clarify that it is a 

ratio of casing to tubing pressure.

 Amend Equation W-9 by clarifying calculation methodology 3 applies to well venting 

not “each” well revising the definition of parameter W to clarify that it is the number of 

wells with plunger lift assist. 

 Amend Equations W-8 and W-9 by replacing the subscript “q” with “p” in SFR to match 

the definition of SFRp and clarifying terms Vp and HRp,q are to be monitored per 

unloading event.

 Clarify that appropriate volumetric parameters in Equation W-10A, namely FRMs, PRs,p, 

EnFs,p, and SGs,p, are at standard conditions by adding the subscript s.

 Clarify that Equation W-10B parameter FVs,p and EnFs,p are at standard conditions by

adding the subscript s. 

 Amend section 98.233 (f) by changing the word “backflow” with “flowback”.
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 Amend 98.233(f)(1) to voluntarily allow for reporters to take more than prescribed 

number of samples by inserting the phrase “at least” in the rule text.

 Amend Equation W-11A and W-11B to insert the word “actual” in the definition of FR 

and add subscript “a”. Clarify the definition of “A” to state “Cross sectional open area of 

the restriction orifice (m2)”.

 Clarify Equation W-12 that the relevant volumetric parameters, namely FRMs, FRs,p, and 

PRs,p, are at standard conditions. Adding a reference to 98.233 (t) in FRs,p to convert FRa

to standard conditions. Renaming the parameter W to N and changed its definition to 

make it applicable to each measured or calculated well completion or workovers.

 Clarify Equation W-13 that the output of the equation is the sum of emissions from all 

completions and workers without hydraulic fracturing within a sub-basin by removing 

the word “a” in front of “gas well venting”.

 Amend parameter Es,N to Es,n in Equations W-14A.

 Revised Ta to Ta,p in Equation W-14B signifying that it is for each blowdown “p”.

 Revise 98.233(j)(5) paragraph description language to clarify that the 10 barrels per day

floor is the annual average daily throughput.

 Revise Equation W-15 to clarify the description of 1000. 

 Revise Equation W-17B to revise the definition of PR to clarify actual and not standard 

conditions.

 Remove and reserve 98.233(n)(7) to harmonize language with reporting requirements in 

98.236 and remove an undesired calculation.

 Remove the summation operator in Equation W-23 and W-27. 

 Amend Equation W-23 and W-27 Es,i to Es,i,m to signify that the emission are calculated 

for each mode-source combination. The parameter definition for Es,i,m has also been 

adjusted to reflect this change.

 Added limits to the summation operator in Equation W-24 and Equation W-28. 

 Revise Equation W-25 to revise the definition of parameter EFi by deleting the term 

“thousand”.

 Amend reference to Table 1-A to Table W-1A in paragraph 98.233 (r)(2).

 Revise 98.233 (r)(6)(ii) to revise the term “meter or regulator” with “meter/regulator”.

 Revise 98.233(t) to clarify that results need not be converted to standard conditions if 

they already reflect standard conditions.

 Revise 98.233 (t)(1) to clarify that emissions or the results of Equation W-11A and 

Equation W-11B need to be converted to standard conditions.

 Revise parameter definition for Es,n in Equation W-33 to clarify that FRs,p is Es,n when 

calculating subsonic or sonic flowrates under 98.233(g). Revise parameter for Ea,n to 

clarify that FRa,p is Ea,n when calculating subsonic and sonic flowrates under 98.233(g).

 Revise 98.233(z)(2)(vi) to reflect the correct means of referring to HHV.

Changes to 98.236

 Amend 98.236 (c)(5)(ii)(D) by making it the average internal casing diameter for all 

wells instead of each well.

 Amend 98.236 (c)(13) (i)(G), (ii)(C), (iii)(C), (iv), and (v)(B) by correcting the units to 

metric tons CO2e for each gas.
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 Amend 98.236 (c)(14) (i)(C), (ii)(C), (iii)(C), (iv), and (v)(B) by correcting the units to 

metric tons CO2e for each gas.

 Amend 98.236(c)(15)(i)(B) by updating the incorrect reference to Equation W-30 to read 

Equation W-30A.

 Amend 98.236(c)(15)(i)(C) by updating the incorrect reference to Equation W-30 to read 

Equation W-30A and by deleting the unnecessary reference to parameter GHGi.

 Amend 98.236(c)(15)(ii)(A) by deleting the reference to 98.230 (a)(4) and Table W-3.

 Amend 98.236(c)(17)(v) by removing CH4 and make the reporting requirement only

applicable to CO2 emissions.

Changes to Emission Factor Tables

 Revise the incorrect title of Table W-1A of subpart W by deleting “TABLE A-1A” and 

updating it to “TABLE W-1A”.

 Revise the pneumatic device emission factors for the Western U.S. in Table W-1A to 

reflect the same changes that were made to pneumatic device emission factors in the 

Eastern U.S.

 Amend Table W-5 to provide the cross-reference for footnote 2 by adding the reference 

to Vapor Recovery Compressor.