### Oil and Natural Gas Sector Synthesis Paper

Peer Review Responses of Environmental Defense Fund

June 16, 2014

EDF appreciates the opportunity to provide peer rev iew responses to EPA’s White Papers, which evaluate emissions of volatile organic compound (“VOC”) and methane emissions from key sources in the oil and n atural gas sector and describe costeffective mitigation measures to reduce these emiss ions. In addition to our responses on each of the individual papers, we provide this synt hesis response to better characterize opportunities across papers and to identify cross-c utting themes that have emerged in our

review.

Our expert review of these White Papers is informed by our growing understanding of the urgent need to reduce emission s of methane and other harmful pollutants from the U.S. oil and natural gas sector . Recently, the Fifth Assessment Report of the Intergovernmental Panel on Climate Ch ange (IPCC) concluded that methane is a much more potent driver of climate cha nge than we understood it to be just a few years ago – with a global warming potential a s much as 34 times greater than carbon dioxide (CO 2 ) over a 100-year time frame, and 84 times greater than CO 2 over a 20-year time frame. Approximately one-third of the anthropogenic climate change we are experiencing today is attributable to methane a nd other short-lived climate pollutants, and about thirty percent of the warming we will exp erience over the next two decades as a result of this year’s greenhouse gas emissions wi ll come from methane. 1 Climate scientists are now recognizing that avoiding catast rophic climate change will require both a long-term strategy to reduce carbon dioxide emiss ions and near-term action to mitigate methane and similar “accelerants” of climate change . As a recent article in the journal

Science stated, “The only way to permanently slow warming is through lowering

emissions of CO 2 . The only way to minimize the peak warming this c entury is to reduce

emissions of CO 2 and [short-lived climate pollutants].” 2

Reducing emissions from the U.S. oil and gas sector is an indispensable part of such a comprehensive climate strategy. Oil and gas facilities are the largest industrial source of methane in the United States, accounting for approximately thirty percent of the

nation’s total methane emissions. 3 Frequently, methane from oil and gas facilities i s coemitted together with other harmful pollutants, inc luding ozone precursors such as VOCs and carcinogenic substances such as benzene and oth er hazardous air pollutants

1 Climate Change 2013: The Physical Science Basis, C ontribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Thomas Stocker et al., eds. 2013).

2 J.K. Shoemaker et al., What Role for Short-Lived C limate Pollutants in Mitigation Policy? 342 Scienc e 1323-24 (2013).

3 EPA, Inventory of U.S. Greenhouse Gas Emissions and Sink s: 1990-2012 (2012)

.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

2 (“HAPs”). 4 And because methane is a valuable commodity, redu ctions in methane emissions often pay for themselves due to increased resource recovery – making methane mitigation a low-cost (and sometimes negative cost) proposition. EPA’s White Papers, taken in context with the feedb ack and supplemental information we provide in our peer review responses , present a compelling overview of the scale and scope of emissions from these sources and support a conclusion that further action could mitigate emissions from each of the so urces discussed in the White Papers. Although some uncertainty persists on the overall n ational emissions from the industry, we have a sufficient understanding of individual so urce types to provide confidence that significant benefits would result from implementing proven, practical strategies for

emission reduction.

This synthesis paper is organized as follows. Part I, below, focuses on national emissions estimates and contextualizes the signific ant mitigation opportunity identified by EPA’s five papers. Part II identifies synergies across the five papers, and Part III discusses continuous improvement.



### I. E MISSIONS 

### , M ITIGATION 

### O PPORTUNITIES 

### , C OST 

### & E FFECTIVENESS

Each of EPA’s White Papers presents detailed inform ation on emissions, mitigation technology, cost, and effectiveness, org anized by discrete, individual source types. Because of this focus, the papers do not em phasize a holistic picture of the national potential to reduce overall emissions from the oil and gas sector through expansive deployment of cost-effective and well-dem onstrated mitigation technologies. One recent and compelling illustration of the natio nal-level opportunity to reduce oil and gas sector emissions through the technologies outli ned in the White Papers comes from ICF’s 2014 cost curve analysis. 5

Table 1, below, presents information on national em issions from our review of the White Papers and underlying data, and Table 2 repro duces ICF’s results from table 4-1 of the cost curve analysis, highlighting the technolog ies EPA evaluated as part of the White Paper process. As we note in our White Paper respo nses, some of the technologies EPA presents provide an enhanced opportunity for emissi ons mitigation, and so certain of these numbers are conservative, though illustrative

.

Nearly all of the technologies EPA evaluated in the White Papers are also evaluated in the ICF Report and contribute signific antly to ICF’s estimate that a 40%

reduction in emissions is achievable in 2018 at a c ost of under one penny ($0.01) per thousand cubic feet of gas produced. Oil tank vapor recovery units and pipeline venting

4 Petron et al. , 2014 A new look at methane and nonmethane hydroca rbon emissions from oil and natural gas operations in the Colorado Denver-Julesburg Bas in, Journal of Geophysical Research: Atmospheres,

online: 3 JUN 2014 DOI: 10.1002/2013JD021272.

5 ICF International, Economic Analysis of Methane Emission Reduction Opp ortunities in the U.S. Onshore

Oil and Natural Gas Industries B-6 (March 2014) [hereinafter “ICF Cost Curve Repo rt”], available at http://www.edf.org/sites/default/files/methane_ cos t_curve_report.pdf.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

3 are not covered, however, and we urge EPA to consid er these technologies as part of its

evaluation of cost-effectiveness. Even so, the sui te of technologies EPA evaluates are capable of reducing methane emissions by nearly 2.9 million metric tons or 37 percent of onshore emissions. This represents 93 percent of t he total cost-effective mitigation potential highlighted in ICF’s report. 6

6 Id. at Table 4-1.ENVIRONMENTALDEFENSEFUND•JUNE16,20144TABLE 1: Summary of Likely Emissions Factors and National Emissions for White Paper Sources.Source TypePotential Rangeof AverageEmission FactorPotentialRange ofNationalAnnual CH4EmissionsSkewedEmissionsDistribution?Assessment1. Equipment LeaksProduction Leaks(non tanks)34 Mscf/yr-well(Allen)190-400 Gg YesAllen et al suggests national emissions from equipment leaks aremodestly higher than GHG Inventory; however there is someuncertainty about disaggregating the activity factors for gatheringsites, which are lumped in with production in the inventory.2. Compressor SealsReciprocating - RodPacking500-2,500Mscf/yrcompressor280-560 Gg YesPer compressor average emissions factor is comparable to orsomewhat higher than GHG Inventory estimate but islimited toemissions in the "operating-pressurized" mode. Lowend ofnational estimate is based on the average of reported rod packingemissions per compressor in GHG RP times number ofreciprocatingcompressors in GHG EI; high end doubles the estimate to accountfor likely emissions in the "idle-pressurized" mode. The high-endtotal for rod packing is roughly 25% of total fugitive emissions fromreciprocating compressors in the GHG EI.Centrifugal - WetSeals1,000-8,000Mscf/yrcompressor90 Gg YesPer compressor average emissions factor is likely much higher thanGRI/EPA estimate. National estimate is based on the average ofreported wet seal emissions per compressor in GHG RP, by industrysegment, times the number of centrifugal compressors listed bysegment in the GHG EI. The estimated 90Gg total forwet sealemissions is approximately 20% of the total fugitive emissions fromcentrifugal compressors with wet seals in the GHG EI.ENVIRONMENTALDEFENSEFUND•JUNE16,201453. Pneumatic DevicesControllers4-30 Scf/hour-device560 - 1,000GgYesEmission factors are for sampled populations of devices inproduction service, not specific device types, as reported by Allen etal, Prasino, Fort Worth, and GHGEI; scaled nationalestimates arestrongly dependent on the assumed population mix.The nationalemission range reported here includes, on low end,the EPA GHGestimate for transmission (210 Gg) added to the GHGEI estimatefor production (330 Gg), and on the upper end, thetransmissionestimate added to the high end reported in Allen etal (830 Gg).Pumps10-30 scf/hour-device35-100 Gg UnclearLow and high end of emission factor approximates the value fromAllen et al and GHGRP and Prasino study, respectively. Nationalestimate from Allen et al.4. Liquids UnloadingUnloading wells thatvent152 - 320Mscf/well274 - 321 Gg YesEstimates of highest emitting wells are a substantial driver ofnational emissions.5. Oil wellsCompletions(Potential Emissions)360 - 10,000Mscf/well44 - 272 Gg Likely, Yes (2)Potential emissions per completion 2 - 4 orders ofmagnitude higherthan current emission factor in GHG InventoryAssociated gas 258 Mscf/well 90 Gg YesEmissions are known with relatively high confidencebut maychange depending on future growth of gas gatheringinfrastructure.6. AggregatedEmissions by SiteProduction Sites (allsources includingtanks, pneumatics,and compressors)400 - 1,500Mscf/yr-siteN/A YesThoma ( 300-1,300 Mscfy/site) and Fort Worth (1500Mscfy/site)studies include tanks, pneumatics and compressors -these reporthigher per site emissions than Allen et al (400 Mscfy/site).Transmission Stations(all sources)15,000-25,000Mscf/yr-siteN/A YesSubpart W reports for 462 Transmission Facilities (no combustionemissions)Processing Plants(equipment leaks)66,000 - 81,000Mscf/yr-siteN/ALimited SampleSizeClearstone I and Clearstone II averages for high- and low-end ofrange, respectively (whole gas)TABLE 2: Mitigation Potential, Effectiveness and Co st of Key Control Strategies*

* Adapted from ICF Report Table 4-1. Highlighted tec hnologies were evaluated by EPA in the White Papers. Because EPA evaluated LDAR in the leaks Whi te Paper and because this practice has broad applicability, we have included LDC Meters and Regu lators even though the White Papers did not explicitly evaluate the distribution sector. Finall y, the $0.66 / mcf reduced is another way to understand our earlier statement that a 40 percent reduction is ac hievable for under one penny of gas produced . The latter simply contextualizes total reduction costs in term s of overall gas production.



### II. C ROSS 

### -C UTTING 

### T HEMES 

### & H OLISTIC 

### O PPORTUNITIES

The White Papers largely evaluate mitigation opport unities by focusing on particular sources and examining emissions, the eff ectiveness of technologies in reducing those emissions, and costs. This approach has many advantages, and as we discuss

above, it demonstrates that there are substantial s ources of emissions in the oil and gasE NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

7 sector and opportunities to reduce those emissions at modest, and sometimes negative,

cost.

Here, we supplement the analysis presented in the W hite Papers by highlighting cross-cutting issues that are common to all of the sources discussed in the White Papers. These cross-cutting considerations provide a fuller picture of the benefits associated with reducing emissions from the oil and gas sector.



### A. Emissions

Because the White Papers focus on average emissions from individual sources or facility types, they may overlook key information r egarding the nature and extent of emissions from the oil and gas sector. 7 In particular, the distribution of emissions acro ss sources, the multi-pollutant nature of these emissi ons, and insights from top-down emissions studies provide important, additional con text for evaluating the effectiveness and benefits of mitigation measures.

First, as we describe in our responses to each of t he Papers, most of the emissions sources in the oil and natural gas sector exhibit a highly-skewed or “fat-tail” statistical distribution, in which a small number of “gross emi tters” account for the vast majority of emissions. Figure 2 shows the distribution of emiss ions sources for compressor rod packing and wet seals, liquids unloading, pneumatic controllers, equipment leaks, and associated gas venting and flaring taken from sever al datasets. The presence of “gross

emitters” is evident for each of these areas.

The “gross emitter” phenomenon has important policy implications. Because the average emission factors used to develop official i nventories may not reflect highemitting sources at the far ends of the distributio n, the “gross emitter” phenomenon suggests that the aggregate benefits of emission mitigation measures may be gre ater than analyses of “typical” facilities would reflect. In addition, the heterogeneous distribution

of emissions indicates that the cost-effectiveness of emissions mitigation can be enhanced by securing reductions at high-emitting sources. L astly, several sources suggest that “gross emitters” can result from maintenance issues and malfunctions, rather than intrinsic source characteristics (like high-emittin g pneumatic devices).

Ultimately, the existence of gross emitters undersc ores that a comprehensive policy to address emissions is critical – one that focuses both on prevention of highemitting, systemic sources like pneumatic devices a nd on detection and remediation of leaking sources using approaches that are well-adap ted to finding the highest-emitting sources and facilities. A well-designed leak detec tion and repair program can help identify routine fugitive emissions such as those d escribed in the White Paper on equipment leaks and can also spot failing pneumatic devices, compressor seals, storage

7 Even so, fugitive emissions of methane from oil an d natural gas sector are the largest industrial sou rce of methane in the United States and the second largest source globally. See EPA. Overview of Greenhouse Gases: Methane Emissions, http://epa.gov/climatecha nge/ghgemissions/gases/ch4.html.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

8 tank control equipment, isolation valves, and other sources which can become egregious

sources if left unchecked. This is an often-overlo oked and important benefit of LDAR that has broad relevance to multiple White Papers.ENVIRONMENTALDEFENSEFUND•JUNE16,20149Figure 2. The relationship of the percentage of sources to the percentage of total emissions for rod packing, wet seals,pneumatic controllers, liquids unloadings, equipment leaks, and associated gas venting & flaring. Rodpacking and wet sealemissions are ranked by compressor, pneumatic controller and equipment leak emissions are ranked by component, andunloading and associated gas venting & flaring emissions are ranked by well averages at the sub-basin/company level. Datasources are the Greenhouse Gas Reporting Program 2012 data (GHGRP) and Allen, et al. 2013 (UT).0%10%20%30%40%50%60%70%80%90%100%0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% of methane emissions% of components or wellsRod Packing (GHGRP)Wet Seals (GHGRP)Pneumatics (UT)Liquids Unloading (GHGRP)Equipment Leaks (UT)Associated Gas Venting & Flaring(GHGRP)E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

10 In addition to these distributional issues, EPA’s W hite Papers do not fully capture the multi-pollutant benefits of mitigating emission s from the oil and gas sector. As EPA continues to evaluate emissions mitigation opportun ities, we urge the agency to consider not just methane and VOC reductions that may result from the measures outlined in the White Papers, but also reductions in HAPs like benz ene, which is a known carcinogen. Indeed, as the ICF Cost Curve Report emphasized, th e same mitigation measures that

would achieve a 40% reduction in methane emissions in 2018 would likewise achieve a

44% reduction in both VOCs and HAPs. 8 Any analysis of oil and gas sector pollution mitigation that focuses on a single pollutant – whe ther that pollutant is methane, VOCs, or HAPs – understates the multiple dividends for pu blic health and the environment that

result from emission reductions in this sector. Ho wever, we do recognize that EPA may ultimately decide to focus on one pollutant as it c onsiders appropriate regulatory and policy responses. If that is the case, an approach focused on reducing methane is likely to achieve the greatest multi-pollutant benefits becau se methane is the most ubiquitous of the three major categories of air pollutants associ ated with this sector, and is emitted in large quantities at every step in the supply chain.

Finally, EPA presented only bottom-up emissions stu dies in the White Papers, and while we recognize these studies often provide direct information on equipment emissions factors, they paint an incomplete picture of overall emissions from this sector. In addition to these bottom-up studies, there have been numerous, recent top-down studies assessing oil and gas sector emissions acro ss large geographic areas. Though these studies cannot attribute emissions to a parti cular piece of equipment, they do provide evidence of the magnitude of basin-wide emi ssions, uniformly suggesting these emissions are substantially greater than bottom-up inventories would predict. 9

Accordingly, evaluating emissions holistically reve als additional, critical information that should inform EPA’s thinking on an y future actions. In particular, the

distribution of emissions across sources, which is generally concentrated in a relatively small percentage of high-emitting sources, suggests that leak detection and repair is an essential complement to one-time emissions reductio n strategies like swapping highemitting for low-emitting pneumatic devices. Moreo ver, the data suggest that addressing these emissions has even greater benefits than EPA projected in the White Papers – both because of the multi-pollutant nature of oil and ga s pollution and because top-down evidence suggests that methane and other co-emitted pollutants may be currently

underestimated.



### B. Technology & Effectiveness

Similarly, the White Papers evaluate the ability of technologies to reduce emissions from specific sources, but this approach, while needed, may inadvertently

8 ICF Cost Curve Report at 4-11 to 4-12.

9 A.R. Brandt, G.A. Heath, E.A. Kort, F. O’Sullivan, G. Pétron, S.M. Jordaan, P. Tans, J. Wilcox, A. Gopstein, D. Arent, S. Wofsy, N.J. Brown, R. Bradle y, G.D. Stucky, D. Eardley, R. Harriss, 2014, Methane Leaks from North American Natural Gas Syste ms, 2014, Science, Vol. 343, 33-35.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

11 overlook ways in which technologies can be leverage d or combined to achieve even greater emission reductions than a source-specific analysis would indicate. Indeed, a holistic assessment of mitigation approaches can re veal the potential for greater control effectiveness in two important ways: 1) broad appli cability – once purchased, certain technologies can be applied comprehensively to vari ous emissions points both within facilities and across the oil and natural gas suppl y chain; and 2) synergies – deploying certain mitigation measures in concert can enhance control effectiveness beyond what either technology could accomplish individually.

1. Broad Applicability

At least two of the mitigation technologies present ed in the White Papers have cross-cutting applications at multiple source types within a facility: leak detection technology, and gas capture technology.

As we describe in our response to the Leaks White P aper, leak detection technologies, like IR cameras, are typically used t o survey potentially leaking components over certain intervals of time. Once pu rchased, however, an IR camera can be used to search for emissions across a broad rang e of potentially leaking components at

the same site, such as:

• Valves and other components. LDAR can be effectively used to identify all manner of component fugitive emissions, including e missions from valves, flanges, connectors and open-ended lines.

• Pneumatic Devices . Emissions associated with malfunctioning devices can be detected and mitigated using LDAR.

• Storage Tanks . Significant emissions are often associated with open thief hatches and pressure relief valves that allow emiss ions to bypass control devices, which can be detected and mitigated using LDAR. Colorado now requires regular LDAR at new and existing storage v essels for this very

reason.

• Compressors . Fugitive emissions from sources other than wet se al degassing or deteriorating rod packing can be a significant s ource of emissions, and ICF found that LDAR at reciprocating compressors could reduce methane emissions by approximately 611,000 metric tons per year in 2018, one of the largest opportunities identified.

Because many of these sources are located at the sa me facilities, including all of them within the scope of a comprehensive LDAR program en tails minor incremental costs when compared to a conventional LDAR program with a more limited scope. At the same time, applying LDAR to this broader universe o f sources has significant potential to identify additional leaks – especially malfunctioni ng equipment that contributes to a “gross emitter” profile – and thereby enhance the t otal cost-effectiveness of LDAR.

Gas capture technologies can also be applied broadl y. Two examples of this emerged in our review of the white papers. First, Reduced Emission CompletionE NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

12 technology, like leak detection technology, is used only for a discrete period of time and therefore can be applied across multiple facilities

. 10 Second, gas capture technologies such as vapor recovery units and closed vent system s (which can re-route gas to compressor air intake or to a combustion device) ca n be applied to multiple sources of vented emissions at a facility. EPA’s discussion i n the Compressor White Paper, for

instance, evaluates the effectiveness of these tech nologies in mitigating rod-packing emissions, but the same technology can be applied t o any source of vented emissions on the site (including open-ended lines, blow-down ven t stacks, storage tanks, and many others). And, as EPA recognized, establishing con nections between additional vented sources and capture technology involves minimal cos ts. 11

2. Synergistic Relationships

Beyond applying mitigation technologies broadly to all emissions sources, deploying these technologies in concert can actuall y enhance emission reduction benefits beyond those expected from the technologies on thei r own. In reviewing the White Papers, we found this to be the case where LDAR cou ld be paired with equipment replacement practices. For instance, the Compresso r White Paper evaluates the effectiveness of replacing reciprocating compressor rod packing at regular, three-year intervals. Because this rod packing wears out, emi ssions increase over time, and therefore regular replacement can help to reduce em issions (anywhere from 35 – 80 percent based on data in the White Papers). This r ate of wear, however, is an average across sources and particular compressors may wear out more swiftly or slowly depending on conditions. Accordingly, coupling LDA R with a rod-packing replacement program can help optimize timing of repairs and rep lacements. We believe LDAR could similarly help to optimize pneumatics replacement, as we discuss in our response to the Pneumatics White Paper.

These synergistic relationships are not evaluated i n the papers and we think they provide important additional benefits (and reductio ns in cost) that only further underscore

the commonsense nature of these measures.

3. Cost

Some of the same cross-cutting features that enhanc e effectiveness likewise reduce costs, either in absolute terms or per-ton o f pollutant abated. The most critical source of absolute cost reduction is monetary savin gs due to captured gas that would

otherwise be wasted. In most cases, EPA’s White Pa pers evaluate these cost savings, which can have important impacts on overall costs. For instance, performing a reduced emission completion at many of the oil well complet ions measured in the UT study would completely recoup costs of the REC technology and result in a net cost savings to the operator.

10 As EPA recognizes, this is also true of completion combustion devices.

11 Compressor Paper at 35.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

13 There are other economic benefits of emissions cont rol technology, however, that EPA’s White Papers do not address. For example, ow ners of equipment in certain segments of the natural gas supply chain do not own the underlying natural gas and so do not realize monetary benefits on account of capture d gas. As the ICF Report notes, however, this captured gas does have broader, econo my-wide value which we urge EPA to consider as part of its evaluation of pollution control measures. ICF concluded that when those economy wide benefits are taken into acc ount, the full suite of reduction strategies resulting in 40% emission reduction woul d actually generate roughly $150 million in net annual savings. 12 In addition, certain control measures, like using plunger lifts to mitigate liquids unloading emissions, resu lt in captured gas but also enhance the productivity of the well. 13 The benefits of enhanced production are identifie d in the ICF Report, but not in EPA’s White Papers, and we encou rage the agency to consider these cost reducing factors as well.

Cost sharing is another important, cross-cutting c onsideration for evaluating costs. In particular, and in keeping with EPA’s em issions and mitigation analyses, the agency often attributes the entire cost of a pollut ion control measure to the specific source being evaluated. For example, EPA’s analysis of LD AR at well production sites in the 2012 NSPS rulemaking assumed that each well site wo uld require its own portable organic vapor analyzer. But this approach grossly overstates costs. As we discuss above, the same technology or practice – whether it be LDA R, RECs, or gas capture at compressors – can be applied to a number of differe nt emissions points and can achieve multi-pollutant reductions. The costs of these pol lution control measures should be evaluated accordingly, spreading them across emissi ons sources and pollutants in keeping with how they are applied in reality.

Ultimately, as Part I concludes, each of the source s EPA identifies in the White Papers are significant and present important opport unities for reducing emissions. In addition to this discrete approach, however, a holi stic view of the sources only underscores the significance of the emissions and t he cost-effective nature of the mitigation measures EPA presents.



### III. C ONTINUOUS 

### I MPROVEMENT

Parts I and II reflect the current landscape of emi ssions, mitigation technology and cost, and as we’ve described, provide a rigorou s foundation for actions to address emissions from the oil and gas sector today.

At the same time, the oil and gas industry is defin ed by continuous improvement in technology – a hallmark of how business proceeds in this competitive space. Consider that just in the last decade – as documented in the EDF Leaks response – innovation in infrared cameras has advanced the technology for le ak detection, permitting swifter, often more comprehensive detection of leaks. Going forwar d, we urge EPA to ensure that

12 ICF Cost Curve Report at 4-10.

13 Id. at 3-18.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

14 actions based on today’s cost-effective technologie s also incorporate flexibility to recognize and develop new advances in technology.

Furthermore, policy making itself is expected to dr ive down compliance cost somewhat from where it is today by increasing produ ction volumes and competition in

the vendor market for detection and control technol ogies. In sum, today’s technology landscape provides a solid foundation for highly co st effective reductions, and if recent history and market fundamentals are a guide, deeper and expansive reductions will become even more cost-effective in the coming years as policy develops.



### IV. C ONCLUSION

EDF appreciates the effort and rigor that EPA has t aken in preparing the White Papers, as well as the opportunity to provide exper t review. We believe that the White Papers provide a sound technical foundation for fur ther regulatory steps to reduce air pollution from the oil and gas sector, and are conf ident that the peer review process will only strengthen the knowledge base to inform effect ive action.

We would welcome the chance to discuss our peer rev iew responses with EPA staff. Please contact Ramón Alvarez on any matters relating to these comments.

Sincerely,

Ramón Alvarez, Ph.D.

Senior Scientist US Climate and Energy Program

Environmental Defense Fund 301 Congress Avenue, Suite #1300

Austin, TX 78701

512-691-3408 ralvarez@edf.org