Environmental Protection Agency (EPA) Methane White Paper 

Oil and Natural Gas Sector Leaks 

INGAA Comments 

1. Introduction 

The Interstate Natural Gas Association of America (INGAA), a trade association of the interstate 

natural gas pipeline industry, submits these comments on the EPA’s technical white paper, “Oil 

and Natural Gas Sector Leaks” (Leaks Paper). On April 15, 2014, the EPA released five 

technical white papers discussing potentially significant sources of emissions in the oil and 

natural gas sector. Specifically, the white papers focus on potential emissions and mitigation 

techniques for methane and volatile organic compounds (VOCs). INGAA is submitting separate 

comments on the three papers (Compressors, Leaks and Pneumatics) that address sources 

applicable to the interstate natural gas transmission and storage (T&S) sector. These comments 

address the Leaks Paper. 

In the Leaks Paper, EPA summarized its current understanding of VOC and methane emissions 

from this source category, and its current understanding of available mitigation techniques and 

the cost, effectiveness, and application of these techniques in the oil and natural gas sector. EPA 

has requested comment on 13 questions related to the contents and conclusions of the Leaks 

Paper. 

INGAA and its member companies have a long history of working collaboratively with a variety 

of stakeholders on numerous greenhouse gas (GHG) related issues, including methane 

quantification and mitigation. As such, INGAA welcomes the opportunity to contribute its 

knowledge of emissions and available control technologies. INGAA commends EPA for 

involving stakeholders and inviting comment on the methane white papers. 

Executive Summary 

INGAA has three general points in response to EPA’s white papers. First, there are significant 

differences in the methane emission estimates produced by EPA’s Inventory of U.S. Greenhouse 

Gas Emissions and Sinks (the National Inventory) and the Subpart W portion of its Greenhouse 

Gas Reporting Program (GHGRP)1

. There also are significant gaps in the information available. 

EPA needs to develop a systematic program to reconcile these differences and fill the gaps in 

order to support further discussion on methane reductions. Second, INGAA recommends 

additional discussion and analysis of the implications, including costs, of potential mitigation 

methods. Finally, EPA should recognize that new information will be available soon to 

supplement this discussion. 

                                                            

1 See http://www.epa.gov/ghgreporting/ and http://www.epa.gov/ghgreporting/reporters/subpart/w.html (Starting 

with the 2011 calendar year for Subpart W, the GHGRP requires pipeline companies to submit annual reports of 

GHG emissions for subject facilities. Pipelines must submit 2014 emission information for the fourth annual report 

by March 31, 2015). 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 2 of 17

In response to the Leaks Paper specifically, INGAA offers the following comments: 

1. EPA should support directed inspection and maintenance (DI&M) as a mitigation 

strategy. It is one of the most efficient and cost effective mitigation strategies. 

2. INGAA recommends EPA review of the Subpart W data to properly understand leak 

frequency and distribution. A growing body of work supports the premise that a few 

larger leaks contribute to the vast majority of emissions.2 

3. INGAA disagrees that all leaks are cost-effective to repair. Many factors influence a leak 

repair decision, including, but not limited to, emission rates, reliability, material and labor 

costs, and schedule constraints. 

4. Available technologies, including optical gas imaging (i.e., infrared (IR) camera) and 

EPA Method 21, are adequate for detecting leaks. EPA should remove ambient/mobile 

remote monitoring as a leak detection technology. It does not identify a specific leak 

source and, therefore, cannot be used for that purpose. 

5. Finally, EPA should acknowledge that one of the benefits of a pipeline safety integrity 

management program is a reduction in emissions. 

INGAA welcomes the opportunity to contribute to this discussion. 

Overview of INGAA Responses 

INGAA has attempted to answer each question to the best of its ability. Due to time and other 

limitations, however, INGAA has not answered all questions fully. For some questions, INGAA 

could not respond completely because this would require a significant long-term effort (e.g., a 

research program) that includes all stakeholders. For example, questions regarding technology 

prevalence, cost implications and technical feasibility impacts would entail an integrated 

research effort to provide a quality, validated and vetted answer. In most cases, however, 

INGAA has provided a thorough response with the information available while noting the gaps 

in existing data. Whenever possible, INGAA offers specific examples of field conditions and 

industry experience. Appendix A provides a quick reference to EPA’s questions on leaks and 

INGAA’s response. 

2. Establish an Open Process that Involves All Stakeholders to Further Examine Methane 

Reduction Issues 

Other than the Natural Gas STAR program, EPA has focused its oil and gas industry GHG 

efforts primarily on quantifying or estimating methane emissions. EPA must consider a number 

of issues, including economic, operational and environmental issues as it moves toward a 

broader methane strategy. 

INGAA envisions a process that is transparent and inclusive of industry and other stakeholders to 

examine issues and potential strategies. This has proven effective at other federal agencies and 

for other EPA regulations. For example, EPA could host technical conferences similar to those 

                                                            

2

 This is often referred to as the “80/20 rule” or “90/10 rule” (e.g., 90 percent or more of emissions are due to 10 

percent or fewer of the leaks). 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 3 of 17

convened by the Federal Energy Regulatory Commission (FERC) to examine critical issues prior 

to initiating a rulemaking.3 

This process would provide an efficient and effective means to advance the current 

understanding of methane emissions and how to design effective programs. As an example, the 

EPA GHGRP is intended to develop improved GHG inventories and to inform policy decisions.4 

Subpart W of the GHGRP addresses T&S segment emissions from vents and equipment leaks, 

and companies have submitted three years of data to date. Data is publicly available for the 2011 

and 2012 reporting years,5 and indicate significant differences between Subpart W reporting and 

the U.S. National Inventory6 for T&S sources. These differences are due in part to differences in 

scope but also other reasons. It is very important that these differences are understood and that a 

single accurate inventory is in place before EPA or industry can develop and implement effective 

and efficient mitigation strategies. These proposed technical conferences or workshops can 

provide EPA and industry the platform to discuss these important issues so that EPA’s future 

methane reduction policies reflect all relevant analysis. 

3. Sources of Information on Emissions and Reduction Opportunities7

 

EPA has requested comment on whether the Leaks Paper appropriately characterizes the 

different studies and data sources. INGAA agrees that it is important to understand the sources 

of methane emissions, how those emissions are measured and reported, what reduction 

opportunities exist (and what is the cost associated with these opportunities). While the Leaks 

Paper provides a summary of several sources of information, the paper does not reflect the full 

breadth of valuable information available to EPA on the topic. Further, while the studies have 

been summarized, they are neither compared nor contrasted with each other or with other sources 

of similar information. It would have been valuable for EPA to provide a tabular summary that 

presents the primary results from each study in common engineering units in order to identify 

data gaps and inconsistencies. While it may not have been the intent of the Leaks Paper to 

compare or contrast information, such an exercise is necessary to determine if a particular study 

appropriately characterizes the data available. Further, a comparison of the studies would help 

identify conflicts and data gaps in the information. 

                                                            

3

 FERC typically holds public technical conferences to gather information on important policy issues and to hear 

potentially competing positions in advance of issuing significant rulemakings. For example, in 2012-2013, FERC 

held a series of technical conferences to explore issues surrounding the increased use of natural gas for electric 

power generation and issues that may impede coordination between the gas and electric industries. After 

considering discussions raised by interested stakeholders at the 2012-2013 technical conferences, and subsequent 

public comments, the FERC initiated two rulemakings that propose to address concerns raised by participants at the 

technical conferences. Technical conferences provide the benefit of educating the regulator and other stakeholders 

on a particular issue and facilitating a structured dialogue where stakeholders can debate the effectiveness or need 

for prospective action prior to the issuance in a proposed rulemaking. Often technical conferences can reveal 

stakeholder support for certain initiatives, identify potential flaws in certain proposals, and identify alternative ways 

to address the regulator’s or stakeholders’ concerns. 

4 See 40 C.F.R. Part 98 (2014). 5

 EPA publishes GHGRP reporting results through its data publication tool, Facility Level Information on 

Greenhouse gases Tool (FLIGHT); see http://ghgdata.epa.gov/ghgp/main.do 6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012, EPA 430-R-14-003 (April 2014). This report 

presents the U.S. national GHG inventory from 1990-2012 for anthropogenic sources (i.e., associated with human 

activity) and is referred to as the “National Inventory” in these comments. The report is updated annually.    7 This section generally responds to Leak Paper questions 1 and 2 (emissions studies and data sources).
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 4 of 17

Due to the limited comment period, INGAA did not have time to develop a definitive analysis of 

the various studies listed or a list of key studies that were not included. However, more detailed 

discussion below provides examples of data gaps or differences in the primary tools that are 

being used to inform the process (e.g., differences between Subpart W reporting and the National 

Inventory). 

In general, INGAA views the Leaks Paper as a summary of some information but not the full 

range of studies and data sources currently available. EPA’s characterization that the studies 

presented in the paper are pivotal suggests that EPA considers them key to understanding these 

issues. INGAA would caution EPA against placing excessive weight on this limited information 

since other studies, not referenced in the Leaks Paper, may be based on the same or similar data 

sets but reach different conclusions. 

INGAA also urges EPA to elaborate on how it arrived at its cost analysis for mitigation 

measures. Cost estimates are sensitive to assumptions and inherent data inconsistencies. Costs 

vary over time and with location and chosen technology. As presented by EPA, the 2014 study 

by ICF, Economic Analysis of Methane Emission Reduction Opportunities in the U.S. Onshore 

Oil and Natural Gas Industries, (ICF paper)8

 appears to be the primary source of information on 

evaluating cost-effective emissions reduction opportunities. However, the ICF paper has several 

limitations such as only including emissions mitigation options for a subset of emission sources, 

only addressing one mitigation technology or work practice for these select sources (i.e., 

alternatives are not addressed), and generally not addressing uncertainties or presenting ranges 

associated with emission mitigation costs and performance. Further, several other sources of 

similar information have not been referenced. In fact, cost-effectiveness has been examined by a 

number of organizations such as the International Petroleum Industry Environmental 

Conservation Association (IPIECA)9 and the Intergovernmental Panel on Climate Change 

(IPCC).10 Cost effectiveness has also been a topic during the United Nations Framework 

Convention on Climate Change (UNFCCC) events. Given the significance of understanding the 

costs associated with various methane reduction technologies in crafting a comprehensive costeffective reduction strategy, the Leaks paper should expand the discussion to describe more fully 

the body of available information, including key parameters and assumptions that impact cost 

analyses. As an example, the differences between Subpart W data and the National Inventory for 

T&S sources affect the calculation for potential achievable reductions and thus have economic 

analysis implications. 

New sources of information soon will become available that will significantly add to the 

understanding of methane emissions and reduction opportunities in the T&S sector. Specifically, 

the Pipeline Research Council International (PRCI)11 is completing a report summarizing GHG 

emission reduction technologies and work practices applicable to natural gas pipeline 

compressor stations. The PRCI work will identify existing and commercially available GHG 

emission reduction technologies and work practices for pipeline compressor stations, as well as 

                                                            

8 Economic Analysis of Methane Emission Reduction Opportunities in the U.S. Onshore Oil and Natural Gas 

Industries, ICF International, 2014. 9

 Oil and Natural Gas Industry Guidelines for Greenhouse Gas Reduction Projects, March 2007 

10 Climate Change 2007, the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on 

Climate Change (IPCC). 

11 The Pipeline Research Council International (PRCI) is the global collaborative research development organization 

of, by, and for the energy pipeline industry. 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 5 of 17

identify technologies in development. The report will evaluate technical and economic viability 

of existing and developmental GHG emission reduction technologies and work practices. While 

this report has yet to be released, PRCI has permitted INGAA to acknowledge the draft 

document for the purposes of our comments. More detail on leak emissions reduction 

technologies and costs is provided in comments below. 

4. National Estimates of Methane Emissions and Methane Emission Factors, Activity 

Data, and Calculation Methodologies12 

EPA has asked for comment on the national estimates of methane emissions and methane 

emission factors, activity data, and calculation methodologies. While there are several sources of 

information on methane emissions from the natural gas system, the two primary sources of GHG 

emission data are the National Inventory and the EPA GHGRP. The EPA compiles both a topdown estimate of GHG emissions (i.e., National Inventory activity data uses data such as facility 

count and miles of pipe to estimate emissions) and detailed bottom-up reporting (GHGRP). 

Using other common vernacular, the National Inventory is commensurate with a Tier 1 or Tier 2 

estimate (i.e., using activity data at the facility or large unit level), while Subpart W of the 

GHGRP uses Tier 3 (more granular source or component level activity data) or Tier 4 (detailed 

source level data or direct measurement) estimates. These two reports use different methods for 

estimating methane releases and do not include all of the same sources of releases. Accordingly, 

there currently is no single compilation that comprehensively and accurately addresses all 

sources of methane released by the T&S sector. 

While the National Inventory and the GHGRP produce consistent estimated emissions from 

some sources (e.g., the natural gas production segment), there are significant differences for the 

other segments of the natural gas system. There likely are multiple reasons for the disparity, 

including differences in the methodologies used in the two programs, and the specific sources 

being measured and included for reporting. For example, EPA updated key National Inventory 

estimates for the production segment based on more recent data, including Subpart W data. In 

contrast, EPA has not yet updated its key estimates for the T&S segment, and it does not appear 

that EPA has compiled or analyzed results based on thousands of measurements for T&S sources 

completed in response the GHGRP reporting requirements. INGAA suggests that the approach 

used for production can also be used to improve the estimates for the T&S sector and to serve as 

a more accurate basis for determining costs and mitigation opportunities. Work to reconcile 

these estimates remains an area of needed analysis before drawing any definitive conclusions 

about the total level of methane emissions from natural gas pipelines or definitively addressing 

related questions about mitigation and costs. 

The need for more current data and analysis on methane emission levels is highlighted by the 

fact that most T&S emission factors used for estimating methane emissions are based on a 

limited set of data that is approximately two decades old. The emission factors that are used to 

calculate methane emissions for both the National Inventory Report and for some Subpart W 

sources, have typically been in place since the 1990s and need to be updated. For T&S, the 

National Inventory (and other published papers and studies) primarily rely on emission factors 

                                                            

12 This section generally responds to Leaks Paper questions 1 and 2 (emissions studies and data sources), 3 and 4 

(emission reductions & leak detection), 5 (impact of facility attributes on emissions), and 6 and 7 (leak detection 

technologies and efficacy). 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 6 of 17

derived from an EPA – Gas Research Institute (GRI) study13 that was completed in the early 

1990s and published in 1996. These factors may not accurately reflect natural gas transmission 

methane emissions because operating practices, as well as the efficiency of operating equipment, 

have improved over the past 20 years. INGAA urges EPA to initiate a program to use the T&S 

data from 2011, 2012 and 2013 GHGRP reporting to support development of improved emission 

factors and improved emission estimates for the T&S segments. 

The GHGRP also has some limitations, including reliance on dated emission factors and 

exclusion of smaller facilities and smaller sources at subject facilities. Subpart W also does not 

require reporting of known sources, such as rod packing emissions in “not operatingpressurized” (i.e., standby) mode, and centrifugal compressor emissions from dry seals. 

However, analysis of the reported data should significantly improve the understanding of 

methane emissions from the T&S sector, especially where measurement is required. Future 

improvements in estimates of aggregated methane emissions, along with use of Subpart W direct 

measurements to update emission factors, can lead to more accurate estimates overall. INGAA 

asks that EPA work with the industry to develop emission factors for the sources with new 

measurement data available. 

Emissions Studies – Leaks Emission Factors, Activity Data and Emission Estimates14 

As noted above, while the emission studies listed in the Leaks Paper provide a sampling of 

available information, other valuable sources are available. For example, the Leaks Paper lists 

two Clearstone Engineering Reports from 2002 and 2006 that are from a collaborative project 

that investigated emissions and the effectiveness of DI&M at processing and gathering facilities. 

These projects were subsequent to the original EPA-GRI study, and there were additional papers 

published in the late 1990s and early 2000s that discussed similar projects at transmission and 

storage facilities. This work included facilities in both the U.S. and Canada. In addition, there 

are reports available that EPA has used for other purposes, such as development of equipment 

leak emission factors used for T&S sources in Subpart W of the GHGRP. Thus, the listed 

sources represent a sample but not an all-inclusive list of available studies and data. For 

transmission, Table 2-4 presents emissions from the EPA-GRI study. We point out that this 

Table does not reflect the data provided in the narrative and has internal inconsistencies that need 

to be corrected. The presentation of data confidence intervals are in this table (and selected 

others) is very helpful and an important consideration. However, confidence intervals are not 

consistently presented and needs to be consistently used to provide a rudimentary understanding 

of the relative accuracies and uncertainties for the various studies. Emission estimate 

uncertainties are an important consideration but methods can vary from report to report. Thus, 

unless each listed report is reviewed in detail, it is not possible to understand accuracy and 

uncertainty for the various studies, so meaningful comment on study efficacy cannot be offered. 

                                                            

13 Methane Emissions from the Natural Gas Industry, EPA/GRI report (June 1996) at: 

http://www.epa.gov/gasstar/tools/related.html; This 15-volume compendium of reports is from an EPA/GRI study 

published in 1996 that remains a seminal reference on methane releases from natural gas systems. These reports and 

related data are referred to as the “EPA-GRI Study” in this paper. 

14 In addition to text above, this section generally responds to Leaks Paper questions 1 and 2 (on emissions), 3 and 4 

(emission reductions and leak detection), 5 (impact of facility attributes on emissions) and 6 (leak detection 

technologies). 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 7 of 17

A more comprehensive list of reports and leak emissions-related documents could be compiled, 

but a higher-priority endeavor might involve a better characterization of the strengths and 

weaknesses of available documents, identifying data or information gaps and defining a 

programmatic approach for resolving discrepancies and addressing data gaps differences. 

INGAA cannot now provide a comprehensive response because there was limited time to 

respond to the white papers. In addition, INGAA believes there is a general need to develop a 

systematic approach for compiling and analyzing information, understanding and reconciling 

differences in available information, identifying data gaps, and developing an agreed up 

inventory. There are also important issues regarding the breadth of each listed study. For 

example, some studies present emissions data or estimates (where emissions data may be from 

other projects) and then add an analysis on mitigation or costs. Thus, not all listed studies are 

original work regarding emission estimates, and there may be issues with assumptions regarding 

mitigation or costs. Also, some of the listed studies are focused on production or other upstream 

operations and not transmission or storage.15 

In general, the studies presented use common and accepted methods for estimating leak 

emissions. Leaks are a more complex and complicated emissions source to understand, but have 

a relatively long history of “accepted” methods. EPA’s focus should be on studies that provide 

original data where leaks are not only detected but also measured, because this provides a more 

complete understanding of leaks. Other emission factor-based data to estimate leak rate can also 

be useful but provide less insight. For example, Subpart W of the GHGRP requires leak surveys 

for transmission, storage, and gas processing. The surveys identify the number of leaks by 

component type (e.g., connector, open-ended line, etc.) and then use a component-specific 

“leaker emission factor” to estimate emissions. With three years of Subpart W GHGRP reports 

submitted to date, many leak surveys have been completed and information on leak frequency is 

available within the Subpart W database. While that data can be insightful as to the prevalence 

of leaks, it does not provide new information on leak rates because emission factors are used for 

the emission calculation. 

At this time, natural gas industry stakeholders are compiling information from Subpart W 

reporting for T&S sources, but have not completed analysis of the data. The compressor-related 

measurements required for Subpart W measure leaks in some cases. Several source types are 

measured in defined compressor operating modes in the compressor measurement program. The 

sources includes vented emissions (e.g., from reciprocating compressor rod packing). As 

discussed in INGAA comments on the Compressor Paper, this also includes sources that are 

considered “leaks” in these white papers, including reciprocating compressor isolation valve 

leakage in shutdown mode, reciprocating compressor blowdown valve leakage in standbypressurized mode and operating mode, centrifugal compressor isolation valve leakage in 

shutdown mode, and centrifugal compressor blowdown valve leakage in operating mode. EPA’s 

methane papers address leaks within the Leaks Paper and compressor venting in the Compressor 

Paper, but there is some overlapping and potentially conflicting content. For example, on page 3 

of the Leaks Paper the reference to compressor seals as a potential leak source is not clear as it 

could be interpreted to mean reciprocating compressor rod packing, which is addressed in the 

Compressor Paper. As discussed in the Compressor Paper, compressor emission factors are 

sometimes a composite that includes leaks and vented emissions. For example, reciprocating 

                                                            

15 INGAA is not familiar with several of these listed studies and does not plan to review documents that are not 

related to the T&S sector. 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 8 of 17

compressor emission factors from the EPA/GRI study include both rod packing emissions 

(covered in the Compressor Paper) and leaks from isolation and blowdown valves (covered in 

the Leaks Paper). The Compressor Paper explains complications and errors that can result when 

using such emission factors to assess baseline emissions and potential reductions. 

Although not readily apparent when reviewing Subpart W reports, direct measurement data are 

available for compressor isolation valves and blowdown valves, because measurement of leaks 

from these compressor valves are required for transmission, storage, and gas processing 

facilities. A project being conducted by the Pipeline Research Council International (PRCI) is 

compiling and analyzing this data. At this time, detailed analysis has not been completed, but 

2011 and 2012 reported data show that over 4,000 leak rate measurements from isolation and 

blowdown valves have been completed at T&S facilities. These measurements are separate from 

rod packing venting and wet seal degassing vent emissions measurement that are the province of 

the Compressor Paper. It is imperative that this measurement data be compiled, analyzed, and 

understood, so that Subpart W results fulfill the GHGRP objective of providing improved 

information to inform policy decisions. Through the PRCI project and related INGAA activities, 

the gas industry will have new and significant additional data to provide to EPA regarding 

methane emissions from the T&S sector. Natural gas transmission stakeholders welcome the 

opportunity to work with EPA on analyzing and understanding these data. 

Subpart W and National Inventory Emission Estimates and Discrepancies 

As discussed in INGAA comments on the Compressor Paper, the grouping of compressor-related 

emissions can cause confusion. Different studies and emission factors may treat compressorvented emissions (e.g., from rod packing) and leak-related emissions from compressor isolation 

valves and blowdown vent valves differently. For the purposes of Subpart W reporting, leaks 

from the isolation valves and blowdown valves (in the associated operating modes) are measured 

and reported as compressor emissions, which also included rod packing (for reciprocating 

compressors) and degassing vent emissions (for centrifugal compressors). Compressor emission 

factors from the EPA-GRI study, conducted in the 1990s, integrate these emission sources into a 

composite emission factor that considers the emission source and time in the related operating 

mode. Emission factors from the EPA-GRI study are used for National Inventory estimates for 

the T&S segments. Separately within Subpart W, (other) emissions from equipment leaks are 

reported, which addresses components, including some compressor related components such as 

fuel lines that are not specifically addressed by Subpart W direct measurement. 

Further, there are disparities in the Subpart W reported results for compressors, with a significant 

difference for centrifugal compressors. At this time, it is not clear how the different sources (i.e., 

vents versus valve leaks) contribute to the disparities. However, it is important to understand the 

data and reconcile differences in the historical estimate from the National Inventory and 

estimates based on recent Subpart W measurements. To summarize the differences explained in 

more detail in comments on the Compressor Paper, when Subpart W results are adjusted (scaled 

up) to use the same activity data as the National Inventory: (1) reciprocating compressor 

emissions are over 50 percent higher in the National Inventory than emissions based on Subpart 

W data; and (2) centrifugal compressor emissions are 20 times higher in the National Inventory 

than emissions based on Subpart W data. 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 9 of 17

Subpart W reports “equipment leaks” based on a leak survey and “leaker” emission factors 

(separate from the compressor valve leakage discussed above) and that data can be scaled up and 

compared with the National Inventory, which uses facility count as the activity data for 

estimating leak emissions from compressor stations. Based on an initial analysis, Subpart W 

data has been compiled from 315 transmission facilities that completed leak surveys in 2011 

(i.e., this is about 1/5 to 1/6 of the total T&S facilities in the U.S.). A direct comparison 

indicates that the equipment leak estimate from the National Inventory is over 14 times higher 

than Subpart W reported emissions. When the Subpart W data is scaled up based on average 

emissions per facility and using the National Inventory facility count, the National Inventory 

estimate is over 2.5 times higher than an estimate based on Subpart W data. 

As noted, data compilation and review are ongoing, and additional insight may be gained that 

can be shared with EPA. At this time, the reason for the discrepancies is not clear. It is also not 

clear how EPA plans to use this Subpart W data to understand emissions and assess whether the 

national inventory estimate should be revised. INGAA members and other industry operators are 

expending considerable resources to complete compressor measurements of vented emission and 

valve leakage, as well as annual facility leak surveys. Thousands of measurements and hundreds 

of leak surveys have been completed to date and ongoing annual measurement is currently 

required. It is imperative that this significant dataset be used to improve the understanding of 

emissions from T&S facilities and inform policy decisions. If not, the GHGRP is not fulfilling 

its objective. 

INGAA recommends that EPA develop a comprehensive, systematic plan to compile, review and 

analyze this data. GHGRP results should be the building block of future emission estimates. 

These data need to be understood, and differences with other data or studies need to be 

reconciled. Until the emission estimates are more clearly understood, it is not possible to 

accurately assess emissions reductions or costs associated with mitigation. 

Finally, INGAA believes that careful review and understanding of new data from Subpart W is 

important to advance the understanding of leak frequency and distribution, which have 

implications for emissions and appropriate mitigation strategies. A growing body of work 

supports the premise that a few larger leaks contribute the vast majority of emissions. This is 

often referred to as the 80/20 rule or 90/10 rule (e.g., 90 percent or more of emissions are due to 

10percent or fewer of the leaks). Many studies support this assertion (e.g., the original EPA-GRI 

study, the EPA-sponsored Clearstone Studies listed in Table 2-1). A clear understanding of this 

phenomenon is needed so that appropriate leak mitigation strategies can be defined. Mitigation 

is discussed further below. 

Emissions Estimates and Leak Detection16

Leak Paper questions 3 and 4 inquire about emissions estimates and associated leak detection 

methods. Emissions estimates are discussed above. Regarding leak detection techniques and 

methods, the Leak Paper adequately discusses the suite of technologies and methods that are 

available. This includes newer technology (e.g., optical gas imaging – i.e., the IR camera) and 

longstanding methods – e.g., Method 21 which includes methods that range from soap bubbles to 

                                                            

16 See Leaks Paper questions 3 and 4 (emission reductions and leak detection) and 6 (leak detection technologies).
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 10 of 17

analyzers (“sniffers”) that measure hydrocarbons. The technologies and methods identified are 

established and adequate for leak detection, and are generally applicable across facility types. 

However, the Leak Paper also includes “ambient/mobile monitoring” as a leak detection 

technology. INGAA understands that mobile monitoring has been used in recent studies to 

identify atmospheric methane and estimate the flux rate (i.e., emissions) attributable to an 

upwind source. While this method/technology may serve a purpose for assessing total emissions 

from a facility or upwind source, it should not be considered a “leak detection” technique, which 

requires the ability to pinpoint specific leaks coming from individual points within a T&S facility 

with hundreds or even thousands of components spread across several acres. As discussed below 

in the mitigation section, it is important for the technique to identify the specific source of the 

leak – i.e., the leaking component – such as Method 21 or an IR camera. Ambient/mobile 

monitoring does not identify the leak source for a T&S facility and, therefore, should not be 

identified as a leak detection technology. 

Question 4 also inquires about ongoing or planned studies. INGAA strongly recommends the 

design and implementation of a systematic, comprehensive study to assess Subpart W data and 

other data to improve the current understanding of emissions. As noted, PRCI is compiling and 

analyzing Subpart W data from transmission companies (i.e., PRCI and INGAA members) and 

that information will aid in the understanding of methane leaks and mitigation practices. 

Several transmission companies are also participating in an emission study with the 

Environmental Defense Fund (EDF). The EDF study includes onsite direct measurement and 

mobile tracer flux measurements of T&S facilities, and results should be available later this year. 

INGAA suggests that a collective effort between EPA and industry is needed to understand 

Subpart W data, other existing data, and these new results so that more definitive conclusions 

can be reached on leak emissions from T&S facilities. 

Factors Affecting Emissions from Leaks 

Question 5 asks about facility types or other attributes that may result in higher leak emission 

rates. INGAA believes that a study would be required to answer this question. INGAA agrees 

that the factors listed by EPA are logical parameters to include in a study design, such as 

equipment type and count, age, maintenance history, and gas quality (e.g., sour versus sweet 

gas), since they could impact leak profiles. 

5. Leak Detection Technology17

The discussion above reviews leak detection technology – Method 21 and IR cameras – as it 

relates to identifying and estimating emissions. The Leaks Paper captures the methods and 

technology commonly used for locating leaks, and these have a long history associated with 

VOC emissions. In recent years, the IR camera has been added as a leak detection tool, and it is 

widely used for the annual surveys required by Subpart W of the GHGRP. 

                                                            

17 This section responds to Leaks Paper questions 3 and 4 (emission reductions & leak detection), 5 (impact of facility 

attributes on emissions), 6 and 7 (leak detection technologies and efficacy), 8 (prevalence), 10 (mobile monitoring and 

optical imaging), and 13 (technology innovation).
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 11 of 17

In general, technologies should be applicable at any type of facility, but some techniques may 

have greater utility at some facility types. For example, an IR camera facilitates leak screening 

of elevated and inaccessible vents that are common at T&S compressor stations. 

INGAA understands that ambient/mobile monitoring is being used in some studies, and some 

INGAA members are collaborating with EDF on a study that uses tracer flux measurement with 

an instrumented van. However, that technology should not be considered for leak detection, 

because for leak detection to be useful it must pinpoint the exact source of the leak. Mobile 

monitoring cannot provide that functionality. 

It is important to note that these technologies and methods are associated with finding leaks. 

Mitigation approaches discussed below include DI&M, which includes measuring leak rates 

when a leak is found. While leak detection technology is relatively robust, leak rate 

measurement approaches such as the high volume sampler and calibrated bag methods are more 

complex and time consuming. Advances in leak measurement technologies are desirable, such 

as advancing the IR camera to provide leak quantification or leak rate approximation and binning 

(e.g., small leak, larger leak worth further scrutiny). At this time, INGAA is not aware of studies 

or research that would develop or improve technology for leak rate measurement. 

In question 10, EPA requests comment on using ambient/mobile monitoring in conjunction with 

IR camera technology for leak detection. INGAA reiterates that ambient/mobile monitoring for 

leak detection at T&S facilities is inappropriate and unnecessary for this application. The use of 

an IR camera is robust and accurate enough to identify leaks quickly and efficiently without the 

need of supplemental ambient/mobile monitoring equipment. Pairing with mobile monitoring 

does not provide useful additional leak information beyond what the IR camera provides, and it 

actually may reduce the effectiveness of a leak detection survey due to its additional resource 

and time requirements. It would also add technology and support labor costs. As discussed 

below, the principles for implementing leak mitigation are fairly well understood, and mobile 

monitoring technology is neither needed nor effective for T&S facilities. 

Finally, question 8 requests feedback on the prevalence of leak detection technologies and 

question 7 inquires about costs and efficacy. INGAA is aware that multiple methods are often 

used for a leak survey depending on the source – e.g., Method 21 to screen leaks, acoustic 

methods to detect through-valve leakage, IR camera for elevated components. However, 

INGAA is not aware of the prevalence or preferential use of certain techniques over others. An 

answer to this question cannot be provided without conducting a survey to understand operator 

practices. There may be reasons to use different technologies within a single survey, depending 

upon the situation. For example, an IR camera may facilitate quicker leak screening but can also 

be limited by weather conditions and other factors. The equipment cost generally is much higher 

than other methodologies available. Method 21 may be preferred in some cases to assess the 

leak relative to a threshold (e.g., 10,000 ppmv). All of the standard methods are viable and used 

in practice, and factors that may affect use for a particular site or survey are best left to the 

specific company to determine the most effective tools to identify leaks for each of their 

facilities. 

INGAA takes issue with some information included in the Leaks Paper, but due to the short 

comment deadline cannot provide a detailed critique of all of areas of disagreement in these 

comments. For example, the paper notes that an IR Camera can monitor nearly two thousand 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 12 of 17

pieces of equipment per hour at a refiner (or over 30 per minute). That is likely an over-estimate 

for most facilities and technology users. 

6. Mitigation Techniques and Costs18

The cost of leak mitigation techniques vary and are generally based on the leak definition and the 

leak repair decision. For example, a Method 21 threshold (e.g., 10,000 ppmv screening value) is 

one basis for defining a leak. Conventional leak detection and repair (LDAR) programs that are 

in place for VOC emissions generally include such a definition. If above the threshold, repair is 

required but qualifiers need to be considered, such as issues associated with elevated 

components, delay of repair criteria, cost and availability of replacement components, additional 

gas venting that would occur when the component(s) are replaced, etc. Another approach that 

differs from LDAR is DI&M, which was used by some voluntary participants in the Natural Gas 

STAR program and is well documented in EPA literature19 and other public domain 

documents.20

For compressor stations, INGAA believes that DI&M considers the key qualifiers and provides 

the flexibility to identify and address the highest priority leaks that warrant repair. DI&M survey 

costs are higher than conventional LDAR because leak rates must be measured using a high 

volume sampler, calibrated bag, flow meter or other appropriate method. The Natural Gas 

STAR Lessons Learned document provides additional detail on DI&M, and INGAA welcomes 

the opportunity to discuss DI&M further with EPA. The premise of DI&M is that typically, the 

largest leaks occur at just a few sources and it is not always economical to repair every leak. 

INGAA agrees because many factors can affect repair costs. Papers that espouse the theory that 

it is economical to repair all leaks were not scrutinized, but perfunctory review indicates that 

questionable or simplistic assumptions were used, such as a single or limited number of costs 

defined for repair. Repairing all leaks is not always prudent since the cost of the repair may far 

exceed the benefit of eliminating a small leak. 

Many factors can affect leak repair costs, which is a reason that INGAA supports DI&M for 

compressor stations rather than LDAR programs based on the premise that any leak should be 

repaired. Factors affecting leak repair costs include: 

• Component type (e.g., valve, pump, rod packing flange, etc.); 

• Component location with the facility (e.g., access, elevation); 

• The ability to repair and action required (e.g., tighten a connection, partial disassembly of 

simple component to replace a gasket, facility shutdown and major equipment disassembly) 

or the need for replacement; 

• Material needs and purchase and delivery times or availability of spare parts; 

• Additional support or material costs; 

• Facility operational constraints (i.e., lost operational time due to the need to shut down or 

isolate the component); 

                                                            

18 This section responds to Leaks Paper questions 9, 11 and 12 (leak mitigation and costs). 

19 Directed Inspection and Maintenance at Compressor Stations, Lessons Learned from EPA Natural Gas STAR 

Partners, EPA430-B-03-008, see: http://epa.gov/gasstar/documents/ll_dimcompstat.pdf (October 2003). 20 For example, see the two Clearstone reports, which were EPA sponsored studies, in Table 2-1 of the Leaks Paper.  
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 13 of 17

• Lost product (e.g., need to blow down equipment for access); 

• Standard labor time required to repair the leak; 

• Engineering design support for more complex replacements requiring piping modifications or 

similar actions; 

• Specialized labor or technical expertise needed for repair or replacement; and 

• Impacts to upstream or downstream operations and customers. 

 

A case-by-case evaluation is needed to better understand the cost implications of a repair 

decision. Some repairs can be made easily and quickly, while others may take considerable 

planning, timing and scheduling prior to implementation. DI&M provides a logical thought 

process for the repair decision and allows operators to focus on larger leaks (as appropriate) 

while also addressing “quick and easy” repairs that may not have high leak rates. 

Some of these factors are considered in LDAR regulatory programs (e.g., 40 C.F.R. 60, Subpart 

KKK) and include provisions regarding repair timing and deferral (e.g., at next scheduled plant 

turn-around). Leak repair programs need to consider these same repair or replacement 

considerations, timing and scheduling requirements. 

The DI&M process is explained in the referenced documents, including existing EPA material, 

and INGAA can provide additional information if needed. A PRCI report is nearing completion 

that provides additional discussion on leak mitigation technologies and work practices and 

associated costs, and that report includes a detailed discussion of DI&M. 

Pipeline Safety Integrity Management Will Reduce Methane Emissions 

Finally, EPA should acknowledge that integrity management programs intended to improve 

pipeline safety have the ancillary benefit of reducing operating methane emissions. However, 

integrity management requirements can also result in additional methane emissions from pipeline 

blowdowns related to maintenance projects. When and where possible, pipeline companies 

employ pump-down and recompression to minimize the release of methane during these 

activities. 

Inline inspection (ILI) technologies that can measure the material strength of pipelines as 

effectively as, or better than, hydrostatic testing would eliminate the need for hydrostatic testing. 

This could greatly reduce the cost and disruption caused presently by such testing to confirm 

material strength and contribute to reducing pipeline methane emissions by eliminating the need 

to remove natural gas from the pipeline prior to testing. To achieve these benefits, it will be 

critical for the Pipeline and Hazardous Materials Safety Administration (PHMSA) to authorize 

the use of the new ILI technology in lieu of hydrostatic testing. 

7. Coordinate Methane Initiatives across Agencies and Establish a Primary Point of Contact 

As part of the Obama administration’s Climate Action Plan, the Administration has initiated 

several efforts that address methane reductions, including revisions to the EPA Natural Gas 

STAR Program, launch of the Quadrennial Energy Review, revision of EPA’s GHGRP, the five 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 14 of 17

methane white papers and plans to revise regulations to control VOC emissions, and possibly 

methane emissions from the oil and gas sector.21 This level of simultaneous activity on a 

common issue challenges the industry and other stakeholders, and coordination between industry 

and between policymakers is crucial. Therefore, INGAA recommends that the Administration 

establish a primary point of contact responsible for ensuring coordination across the multiple 

federal agencies and departments tasked with methane-related initiatives impacting the T&S 

sector. Ideally, this point of contact would provide guidance and assistance in the development, 

interpretation and implementation of methane policies. It can be difficult for the pipeline 

industry to manage the numerous and sometimes duplicative requests for information from 

multiple agencies and departments. 

As questions arise about the overall climate change strategy, it would be extremely helpful to 

have this same primary point of contact within the Administration to discuss methane and other 

GHG reduction issues, opportunities and policies. 

8. Conclusion 

INGAA and its members are committed to reducing methane emissions in a prudent and 

environmentally responsible manner, and are undertaking initiatives to understand the sources of 

T&S sector methane emissions and identify the most significant sources and the most costeffective methane emission reduction strategies. In summary: 

1. EPA should support DI&M as a mitigation strategy. It is one of the most efficient and 

cost effective mitigation strategies. 

2. INGAA recommends a careful review of the Subpart W data to properly understand leak 

frequency and distribution. A growing body of work supports the premise that a few 

larger leaks contribute to the vast majority of emissions. 

3. INGAA disagrees that all leaks are cost effective to repair. Many factors influence a leak 

repair decision, including, but not limited to, emission rates, reliability, material and labor 

costs, and schedule constraints. 

4. Available technologies, including optical gas imaging (i.e., IR camera) and EPA Method 

21, are adequate for detecting leaks. EPA should remove ambient/mobile remote 

monitoring as a leak detection technology. It does not identify a specific leak source and, 

therefore, cannot be used for that purpose. 

5. Finally, EPA should acknowledge that one of the benefits of a pipeline safety integrity 

management program is a reduction in emissions. 

                                                            

21 For example, potential revisions to 40 C.F.R., Part 60, Subpart OOOO. 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 15 of 17

INGAA appreciates the opportunity to comment on the Leaks Paper and will continue to provide 

EPA with additional information as it becomes available. 

Sincerely, 

Lisa S. Beal 

Vice President, Environment and Construction Policy 

Interstate Natural Gas Association of America 

 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 16 of 17

Appendix A 

Question and INGAA Response 

1. Did this paper appropriately characterize the different studies and data sources that quantify 

VOC and methane emissions from leaks in the oil and natural gas sector? 

Responses are found in sections three and four of the INGAA comment document. 

2. Please comment on the approaches for quantifying emissions and on the emission factors 

used in the data sources discussed. Please comment on the national estimates of emissions 

and emission factors for equipment leaks presented in this paper. Please comment on the 

activity data used to calculate these emissions, both on the total national and regional 

equipment counts. 

Responses are found in sections three and four of the INGAA comment document. 

3. Are the emission estimating procedures and leak detection methods presented here equally 

applicable to oil and gas production, processing, and transmission and storage sectors? 

A limited response is found in section four and five of the INGAA comment document. 

4. Are there ongoing or planned studies that will substantially improve the current 

understanding of VOC and methane emissions from leaks and available techniques for 

detecting those leaks? Please list the additional studies you are aware of. 

A response is found in section four and five of the INGAA comment document. 

5. Are there types of wells sites, gathering and boosting stations, processing plants, and 

transmission and storage stations that are more prone to leaks than others? Some factors that 

could affect the potential for leaks are the number and types of equipment, the maintenance 

of that equipment, and the age of the equipment, as well as factors that relate to the local 

geology. Please discuss these factors and others that you believe to be important. 

A limited response is found in section four of the INGAA comment document. 

6. Did this paper capture the full range of technologies available to identify leaks at oil and 

natural gas facilities? 

Responses are found in sections four and five of the INGAA comment document. 

7. Please comment on the pros and cons of the different leak detection technologies. Please 

discuss efficacy, cost and feasibility for various applications. 

Responses are found in sections four and five of the INGAA comment document. 

8. Please comment on the prevalence of the use of the different leak detection technologies at 

oil and gas facilities. Which technologies are the most commonly used? Does the type of 

facility (e.g., well site versus gathering and boosting station) affect which leak detection 

technology is used? 

A response is found in section five of the INGAA comment document. 
INGAA Comments on EPA Leaks White Paper 

June 16, 2014 

FINAL 

Page 17 of 17

9. Please provide information on current frequencies of revisit of existing voluntary leak 

detection programs in industry and how the costs and emission reductions achieved vary with 

different frequencies of revisit. 

A response is found in section six of the INGAA comment document. 

10. Please comment on the potential for using ambient/mobile monitoring technologies in 

conjunction with OGI technology. This would be a two-phase approach where the 

ambient/mobile monitoring technology is used to detect the presence of a leak and the OGI 

technology is used to identify the leaking component. Please discuss efficacy, cost and 

feasibility. 

A response is found in section five of the INGAA comment document. 

11. Please comment on the cost of detecting a leak when compared to the cost to repair a leak. 

Multiple studies described in this paper suggest that detecting leaks is far more costly than 

repairing leaks and, due to generally low costs of repair and the subsequent product recovery, 

it is almost always economical to repair leaks once they are found. Please comment on this 

overall conclusion. 

A response is found in section six of the INGAA comment document. 

12. If the conclusion is correct that it is almost always economical to repair leaks once they are 

found, then how important is the quantification of emissions from leaks when implementing 

a program to detect and repair leaks? 

A response is found in section six of the INGAA comment document. 

13. Please comment on the state of innovation in leak detection technologies. Are there new 

technologies under development that are not discussed in this paper? Are there significant 

advancements being made in the technologies that are not described in this paper? 

A response is found in section five of the INGAA comment document.