Questions Regarding FWNGAQS

8/3/2019 Questions Regarding FWNGAQS

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Fort Worth Natural Gas Air Quality Study . . . a critical review by Andy Mechling

8.03.2011

Ambient Monitoring Study

An exercise in looking the other way

Here once again, some of the most obvious and important findings from a

major air quality study in the Barnett Shale are seen to revolve aroundmeasured concentrations of carbon disulfide gas; and yet again, therelevant facts need to be pieced together from information buried in thedata tables; as this subject is completely ignored in the narrative sectionsof the final report released to the public.1

Some truly impressive science was brought to bear in this FWNGAQ

study. In the ambient monitoring phase especially, highly sensitivemonitoring methods were utilized in systematic fashion at carefullychosen locations over a two month period, and a mountain of highquality data was generated.

The Eastern Research Group(ERG) team crunched these numbers hard;of course. A variety of statistical screening tools were put to effectiveuse, and as a result; a very interesting picture snapped into focus rightaway. We gained some valuable information here, to be sure.Unfortunately, only some of this makes it into the report.

The ambient monitoring phase looked at 138 chemicals. One of thesecompounds behaves unlike all the rest, and this information is quicklyshaken out through the statistical analyses. Somehow, this fact doesntget discussed.

Even if toxicological concerns are completely ignored, and those 138compounds are treated anonymously; these numbers for CS2 clearlybehave differently than the others; and not just by a little bit.

I am not a statistician. I hold no formal scientific credential of any type.2With all due respect to the scientists involved however, I believe it is clear

that the authors failure to include any discussion of the implicationspresented by their own statistical analysis of the carbon disulfidecanister data represents both a glaring omission, and an obviousproblem with the FWNGAQS final report.

Further, I believe that any serious independent review of the datasets inquestion will identify this exact same issue.


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Straight to the charts - Always

The rubber finally begins to find the road here a little bit in Table 5.2-3.ofthis report. 3 In this table, measured concentrations of target

compounds are compared to TCEQ long-term health effects screeninglevels.

Program-Average Concentrations and TCEQ Long-Term Screening Levels

Compound Site Highest studyaverage (ppb)

Long termscreening level (ppb)

Type

Benzene S-4 0.69 1.4 AMCV

Carbon disulfide S-5 0.94 1 ESL

Carbon tetrachloride S-1 0.12 2 AMCV

Formaldehyde S-4 1.14 8.9 AMCV

The table above was assembled by me and is based directly on table 5.23 on pages 241245 of the report, which

includes entries for all 138 study target compounds. The reader is encouraged to view the full table

"Key Point: Key PollutantsThe key pollutants, based on the ambient monitoring data, were: Acetaldehyde

Benzene1,3-ButadieneCarbon tetrachloridepDichlorobenzeneFormaldehyde (and)

Tetrachloroethylene4

If a reader were to consider only the data in this table; and disregard the

narrative sections or key points presented in this report, he or shemight logically conclude that measured levels of carbon disulfide presentas much cause for concern as any compound identified in this study.

The other three chemicals presented above are all identified as keypollutants during this study. In previous studies, we have seencalculations presented for percentage of screening level. In this study,ERG chooses not to provide these types of figures.

It also seems worth noting that if the ERG team had decided to

incorporate the same protocols as utilized in the 2010 TITAN report,where individual 24 hour canister measurements were used for

comparison to TCEQ long-term standards; the present study would thenhave included several measurements of CS2 from site 5 over that 1ppblong-term ESL.5


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24hr samples represent short-term exposures now?

In the TITAN study and others, short-term health screening levels arecompared to 1-hour concentration data. Here in the FWNGAQS; those

same short-term screening levels are referenced in comparison to 24-hour data.

I do not feel qualified to comment on the relative merits of eitherapproach. Either way though, whether its TITAN measuring CS2 at100% of its short-term ESL, or ERG measuring CS2 at 94% of the long-term ESL, (my math) I believe the public would be better served if thesefacts were discussed, rather than buried, in these reports.

More disappointing than the continued failure to acknowledge potentially

troubling levels of carbon disulfide gas detected in the neighborhoods is

the fact that this compound was monitored only at sites 1-5, and not atany of the other 350+ locations where air monitoring activities were

conducted in this study.

As the researchers got closer to the natural gas sites, they simplystopped monitoring for CS2 altogether. Carbon disulfide was notincluded on the list of chemicals to be monitored at the fenceline sites(sites 6 & 7) in the ambient monitoring portion of this study, and wassimilarly excluded from all lists of target chemicals during the extensive

point source evaluation phase.

Perhaps most disappointing of all is the fact that no true sulfur gas

analysis was performed at any point during this million-dollar air study.Because of this, some highly toxic gases associated with natural gas

production, especially hydrogen sulfide and carbonyl sulfide werecompletely and intentionally overlooked; and important opportunities formethod validation were missed.

.

Study in General

My comments above notwithstanding; I regard this as a vitally important

air study of the very highest quality.I admit to some positive bias coming in. A decade ago, I had theopportunity to work with consultants from ERG on an EPA grant projectinvolving fenceline monitors at a California oil refinery. On that project,the decision to bring in ERG as consultants for the final phases camefrom the EPA Region IX offices in San Francisco.


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From my perspective; the ERG team on that project more than lived upto its billing as top dogs in this field. I came away thoroughlyimpressed with both the capabilities and professionalism of this outfit.

The FWNGAQS, authored by ERG, actually represents an amalgamationof two separate air studies with distinctly different objectives. Theambient monitoringphase and the subsequentpoint-source emissions

evaluationutilized different (but sometimes overlapping) analytical labs,instruments, field methods, target chemicals, sub-contractors, and soon.

Both of these air studies represent scientifically complex and logisticallydemanding projects in their own right. Along with the two monitoringprograms, this report provides other technical guidance; includinganalysis of regulatory issues, emissions modeling, estimates of gasreserves, and a host of other issues involving natural gas production inthe Fort Worth area.

As a whole, I find this 320 page final report, along with the interim report

that preceded it, to be exceptionally well-written. If there are any factualerrors or inconsistencies associated with the narrative sections or tables;I did not find them. Throughout the report, the authors do an excellentjob of presenting some highly complex subject matter in direct and easy-to-understand language.

As air monitoring reports go, this one is also particularly wide-ranging inscope. The authors touch on a number of subjects where I have no

expertise whatsoever. I cannot comment, for example, on the adequacy

of ERGs estimates of remaining gas reserves in the Barnett Shale, or onhow the price of natural gas might factor into estimates of futurepollutant concentrations in the region.

I have only very limited experience working with dispersion models. Icant offer any opinions as to the relative quality of modeledconcentration values in the point-source testing phase of the project; orprovide any type of meaningful insight into analysis regarding the

adequacy of existing setback distances performed by ERG.

My primary interest in this study is focused on the results of sampling

from the ambient monitoring phase; specifically, on the results of theVOC sampling from sites 1-5. These were the only samples analyzed atthe (ultra-capable) ERG lab in North Carolina; and also represent theonly samples analyzed for CS2 at all during the course of this study.

Uneven data quality noted and accepted


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Ambient canister samples from the two fenceline sites were sent to theTest America/Austin lab for analysis. Carbon disulfide was left off thelist of target compounds to be analyzed via GCMS/TO-15 at these sites(6&7).

Even though the concentration data is more spotty in nature, and clearlyof lower quality by comparison; ERG incorporates the results from sites 6

and 7 with all the data from their own lab, and attaches equal weight tothese figures in the various statistical routines employed during thisphase of the study.

The authors make clear note of the differences in data quality, but thendemonstrate that even with the lower quality data from the fencelinesites added into the mix, the project was still able to meet stated DataQuality Objectives (DQOs) across the board.6

For my purposes, I chose to consider results from the two labs

separately.

In one of the findings from the ambient monitoring phase, the authorsexpress surprise at the low nature of some of the concentrationmeasurements from sites 6 and 7:

Pollutant concentrations at Sites S-6 and S-7 (located in a medium-level activityarea) were surprisingly low relative to other sites, especially given their closeproximity to active well pad locations. 7

VOC data: Sites 1-5

At first glance, the concentration data presented in these tables appearsvisibly different than most; due to a conspicuous lack of non-detect data.Seemingly, most of these chemicals are being detected most of the time.Dozens of the target VOCs analyzed under TO-15 are detected in everysample from every site.

Quality assurance figures included with the final report confirm that the

accuracy, precision, and sensitivity demonstrated by the ERG labthroughout the ambient monitoring portion of the study are uniformly

outstanding.89

For the compounds of most interest, including CS2, detection limits are

considerably lower than we have seen in previous monitoring studies inthe region. Typically, the MDL figures demonstrated by the ERG labextend into the low parts-per-trillion range. Generally, these figures runbetween one and two orders of magnitude better than what we havecome to expect from other labs.


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For what it matters, the extensive data set assembled through theambient monitoring portion of this study is undoubtedly the mostimpressive set of air canister data I have ever seen.

Because this study was so effectively implemented; and because thereare actually numbers in those database tables, (as opposed to cells full ofnon-detect data), this project provides unique opportunities for

researchers to identify potentially meaningful trends among the 15,000data points generated here.

Carbon disulfide vs. carbon tetrachloride: Old buddies on opposite sides?

Carbon disulfide and carbon tetrachloride are two substances whichhave plenty in common, and its not all good. Both of these are highly

useful industrial solvents of the highly toxic variety, and they share a

great deal of interesting history.

In the context of this FWNGAQ study, while both of these compounds aredetected in every sample; (sites 1-5) these two historic bad actors find

themselves at opposite ends of the scale - in terms of how their measuredconcentration values are dispersed across the monitoring network.

As explained in some detail in the Interim Report, one of the statisticalscreening tools incorporated by ERG included the calculation of a

Coefficient of Variation ratio (CV) for each chemical detected in at least70% of samples.

The CV ratio is the standard deviation divided by the mean, and is used tocompare the relative dispersion in one set of data with the relative dispersion of

another set of data. The lower the CV ratio, the less variability in the datameasurements.

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From my perspective, the overall picture that emerges from ERGs

statistical analysis of this data set is as surprising as it is crystal clear.In the case of these two solvents especially, it is the consistent nature of

the data, and the clear-cut nature of the trends observed, that I find socompletely unexpected and remarkable.

Carbon Tetrachloride: CV ratio 0.14

Carbon tetrachloride, detected in every sample, is one of those chemicals

whose levels are seen to vary the least across the entire monitoringnetwork during the course of the study. The CV ratio of 0.14 calculatedfor carbon tetrachloride is 5th lowest in this study.


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It is worth noting also that much of the variability that is observed forcarbon tetrachloride comes in the form of slightly depressed readings atsites 6 and 7. If the lower quality data11 from these two sites is left out ofthe calculations, carbon tetrachloride levels appear even more

remarkably stable. (I did not attempt to calculate a new CV ratio basedonly on the data from sites 1-5.)

Study Average Concentrations By Site (ppb)12

The following is included on a list ofKey Findingsin the ambient

monitoring section of the report: 13

ERG found little variability across the sampling network for certain pollutants,such as carbon tetrachloride, chloroform, chloromethane, crotonaldehyde,dichlorodifluoromethane, dichlorotetrafluoroethane, ethylene, 1-hexene, isoprene,propylene, trichlorotrifluoromethane, and trichlorotrifluoroethane. The lowvariability across the entire network suggests that these pollutants are not affectedby localized, anthropogenic sources, but rather exist as background pollutants.

A solid wall makes a solid argument

The authors present a very convincing argument here, in my opinion.The levels of all of pollutants on this list are so remarkably stable and

uniform at the various locations across town, and under various windconditions, and over the course of the study that even from a common-

sense point of view; it is hard to imagine how the presence of these

Location Carbon Tetrachloride Carbon Disulfide Benzene

Site 1 0.118 0.043 0.245

Site 2 0.117 0.034 0.300

Site 3a 0.118 0.050 0.301

Site 3b 0.115 0.013 0.165

Site 4 0.113 0.119 0.686

Site 5 0.108 0.944 0.197


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chemicals could ever be attributed to any specific source - local orotherwise based on these observed trends.

The finding above is entirely consistent with findings published in otherrecent studies. In this case, and for these chemicals, the favorablefinding for industry appears to be based on some very solid science. Thefact that local NG activities are not seen as major contributors to

ambient levels of these pollutants represents valuable information inevery sense. This truly is good news.

It stands to reason that the ERG team might also have been interested inconsidering those chemicals which were seen to display high variabilityacross the network, and for which elevated concentrations might beassociated with proximity to NG activities.

The following appears as a bulleted item on page 18 in a short list underthe heading:

Data obtained from this ambient air monitoring network can be used to:

Characterize exposure to selected air toxics in ambient air at various locations inthe city, as related to the proximity to certain natural gas activities (well pads,compressor stations, fracturing operations, etc.).14

It is interesting to see this type of exposure characterization task showup on a list of things that the data might be used for, rather than as a

primary program objective, or some sort of project deliverable. In anycase, no discussion of source characterization for carbon disulfide isincluded in either the interim or final version of the FWNGAQS report.

The fact that the authors chose not to explore the other side of the coinhere is puzzling; and imparts an unfinished feel to a study whichotherwise appears to be logically presented.

The other side of the coin.

Carbon disulfide appears on the far opposite end of the scale of CVvalues in this project from carbon tetrachloride. The study CV ratio forCS2 is calculated at 1.61; which ranks second-highest behind only the1.84 figure calculated for toluene.


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Toluene: CV ratio 1.84

While concentration values reported for toluene were somewhat morevariable overall than those for CS2, elevated readings for this compound

were far more sporadic in nature; and clear patterns are difficult todiscern.

For example, with toluene, the highest concentrations overall wererecorded at site 2 (near the freeways); whereas on most days, the highest

level across the network was recorded at site 4 (municipal dumpsite). Onthe final day of sampling, the highest concentration of toluene wasmeasured at site 1. (away from the well pads)

Carbon Disulfide: CV ratio 1.61

By contrast, the pattern observed with respect to measured

concentrations of carbon disulfide is absolutely clear and unambiguous.The numbers, in-and-of themselves, may not be too startling, especiallyas measurements at-and-around this 1ppb screening level are roughly inline with results from other recent studies performed in the region.

The concentration figures from this ambient monitoring phase werefinalized and released with the Interim report in February; and the gasindustry has already responded by repeatedly downplaying thesignificance of these numbers.

Fortunately, the scientists involved in this study chose to utilize a

method which was sensitive enough to detect the full range of CS2concentrations encountered; and the study was designed thoughtfullyenough to allow the researchers to put this sensitivity to effective use.

"Key Point: Measurement SensitivityThe ambient air monitoring program used highly sensitive measurement methods. For all buttwo pollutants, the methods were capable of detecting air concentrations at levels belowTCEQs most protective health-based screening values. Therefore, the air pollutionmeasurements were sensitive enough to support health evaluations.15

For measured concentrations of carbon disulfide, it is the way thenumbers are distributed across the sites, even more than the numbersthemselves, which becomes so interesting and revealing.

Even If they did choose to leave it out of their report; the ERG teamclearly deserves credit for producing what is - upon close inspection - afairly elegant piece of science in this project.


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If youre from Fort Worth, and youre trying to find that million dollars; Isay its right here. Buried deep.

Please consider:

Site 5 is surrounded by NG activity - by study design16

Site 5 recorded the highest level of CS2 on every day sampling

occurred there by a convincing margin.

Site 4 was also located near a few well pads.

Site 4 recorded the second-highest level of CS2 on 18 of 19 sampledays.

The lowest 24-hr level recorded at site 5 was 0.492ppb on 10/28.

The highest level recorded anywhere else during the two-month

period was barely half of that. (0.258ppb on 9/10 @ site 1)

The average level of CS2 recorded at site 4 (0.119ppb) is more than

double that of any other site. (excluding site 5)

The average level of CS2 recorded at site 5 (0.944) is more than 7times greater than the level recorded at site 4.

Sites 1, 2, and 3b all recorded at least one 24-hour period withconcentrations at or below 0.010ppb. Seven such days are

recorded between these 3 sites.17

Of the 138 chemicals sampled during this study, none can be

associated with a particular site in anything resembling themanner in which carbon disulfide is associated with site 5.

Besides the situation with CS2, air quality at site 5 generallyappears to be as good or better than at the background sites.Please notice that site 5 reports the lowest average concentration ofbenzene of any of the fixed locations during the course of thisstudy.

Variability at each site explored.

Besides examining the variability in measurements across the network

for those chemicals detected most often, the researchers were alsointerested in looking at the variability displayed by each chemical at eachlocation over the course of the study.


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Pollutant CV Ratios at Each Monitoring Site18

(condensed)

Compound S-1 S-2 S-3 S-3a S-4 S-5 S-6 S-7

Benzene 0.51 0.29 0.56 0.17 0.69 0.37 0.51 0.52Carbon disulfide 1.29 1.04 1.40 0.33 0.40 0.34 NA NA

Carbon tet 0.10 0.09 0.08 0.07 0.11 0.21 0.16 0.15

Individual CV ratios were calculated for all detected chemicals at eachsite. Some interesting patterns emerge. Please notice:

Benzene levels are somewhat variable at all sites. The highest

variability occurs at site 4, (the dump) which is also where thehighest concentrations are recorded. This pattern is typical of

many chemicals in this study.

Carbon disulfide levels are least variable at the sites that recordthe highest concentrations, and most variable at those sites wherelower levels are measured. (and which are farther removed fromNG activities) No other chemical is seen to act like this at all.

CV ratios remain low for carbon tetrachloride across the network.

Are these concentration figures for CS2 under-reported?

The ERG lab detected carbon disulfide in 92 of 92 samples in this study,

at concentrations ranging from 0.008 to 1.64ppb. Because thesesamples were collected using stainless steel Summa canisters, I believethere is some reason to suspect that all of these figures might besignificantly under-reported.

The tendency for sulfur compounds to react with and degrade insidestainless steel canisters is well documented; and the interested readershould be able to find ample literature on this subject.

The following passage appears on the website for Columbia Analytical

Services, a leading analytical lab specializing in sulfur gas analysis:

Since many sulfur compounds are not stable in stainless steel canisters,such as Summa canisters, air samples for this analysis should be collected inTedlar bags. When the odor is intermittent, unpredictable, or at a remotelocation, Columbia Analytical may recommend the use of a Silco (glass lined)canister. Please contact the lab for more information on sampling media forsulfur compounds.


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Due to the unstable and reactive nature of many sulfur compounds, fullcompliance of the method requires analysis of the samples within 24 hours ofcollection.

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When the California Air Resources Board monitored carbon disulfideemissions at a series of agricultural fumigations in 2006, they chose to

utilize Silco canisters in place of Summa canisters.20 The full report,which includes a description of the sampling methodology, is available

on-line.

Based on my own experiences collecting field samples for sulfur gasanalysis; and on the results of recent studies published by TITAN,Kleinfelder, and others; I suspect that the concentration figures for

carbon disulfide presented in the FWNGAQ study probably are under-reported to some degree.

I personally dont view this as an insurmountable problem, or as a majorissue with this report. Here is the crux of the matter in my view:

The ERG lab has been able to demonstrate the sensitivity to detectand quantify carbon disulfide in every sample across an extendednetwork - with precision.

This type of capability has not been demonstrated in previous airstudies conducted in the Barnett Shale.

We know we need better numbers - even if were not sure what they mean.

If we get better information in the future, and if these concentrationfigures are eventually seen as needing adjustment in some direction,then thats terrific, in my view. Better data is always good.

In the case of CS2; I think it is fairly clear that different field methodsmight be expected to yield significantly different results at this point.

Hopefully, this will not be used as an excuse to stop monitoring for thischemical.

It is important to keep in mind that due to gaps in the knowledge baseregarding carbon disulfide, US EPA and ATSDR have been unable to


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establish a dose-response relationship in humans,21 and that betterinformation is clearly needed in this area as well.

Point-Source Emissions Evaluation

A very different animal

Subsequent to the ambient monitoring phase, ERG contracted with SageEnvironmental Consulting LP. (SAGE)to perform extensive leak detectionand air sampling work at NG facilities throughout the FW area.

The point-source evaluation team took to the field equipped with IR

imaging gear, hydrocarbon sniffers, and other specialized samplingequipment for the purpose of identifying leaks and characterizing

emissions of various types at natural gas production facilities.

Objectives for this phase of the project included attempts to calculateTOC, VOC, and HAP emissions rates for each of the 388 sites visited.Air monitoring activities were driven by the leak-detection activities, andsampling protocols were built around efforts to obtain representative airsamples from several different types of detected sources.

This point-source emissions evaluation was another enormousundertaking; which was also well documented and explained in the

report. The actual emissions monitoring that occurred in support of thisproject was very different in nature to what occurred in the ambientphase, although Summa canisters and the TO-15 analytical method were

utilized for some of the samples collected at some of the sites.

The list of VOCs included for analysis is this phase was far more limitedthan in the ambient study, and did not include CS2.22

The innovative study design incorporated by ERG and SAGE included acombination of hi-tech gadgetry, complex math, down-and-dirty

monitoring techniques, and a ton of leg work. Every site was scannedend-to-end with infrared imaging equipment; every fitting and every valve

was accounted for; and all of this was documented in the report.

This point-source study is fascinating for a number of reasons, andseems to reflect some new thinking. The fact that researchers found itnecessary to make key modifications to the monitoring plan during the

course of the study reflects both the novelty of the study design, and theambitious nature of the project as a whole.

I have some general comments about this phase of the project, and Iwould like to make a few things clear before I continue:


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All of my comments are based on my reading of the FWNGAQS.

I have not reviewed any of the supporting documentation, labreports, IR video files, etc.

I have no expertise in dispersion modeling or estimating emissions

rates.

I think this was a cool study.

I wish they had included some testing for sulfur compounds

.

Another Big Step Forward

The amazing thing, which seems almost unbelievable really, is that theydid this at all. Teams went into the field, scanned everything with IR,

sniffed out leaks, counted valves, named names, and then made all ofthe data available to the public in this report, including IR video clipsapparently. Bravo; I say.

If some of their data inputs might have left a little to be desired; at leastthe point source team used consistent methodology throughout the

study, and attempted to maintain a level playing field in this way. Duringthe study, the team identified emissions from 252 tank thief hatches,175 storage tank vents, and 489 leaking pneumatic valve controllers.

The point source emissions team made some important findings as to the

relative makeup and magnitude of these tank vs. non-tank emissions.23

The researchers also quickly determined that the IR imaging devices were

capable of detecting more emissions than they had anticipated; andneeded to scale down the monitoring plan accordingly, as the original

sampling protocols would have required considerably more canistersthan the project had budgeted for. 24

Emissions Rate Estimates

Because no sulfur species were included in the monitoring for this phaseof the project, and especially because only some types of emissionssources were considered, its hard to know just what to make of some ofthese estimates of facility emission rates.

It seems pretty clear that the methodology employed by the point sourceemissions evaluation team was better suited to the well pads, of whichthey visited 375, than to some of the more complex facilities on the list.


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In the case of the lone gas processing facility that was visited, entirecategories of emissions were ignored, including those from vent stacksand flares. This facility, the Crosstex Amine Treatment Center, wasestimated to release 80 tons per year (tpy) of VOC emissions, andrepresents the single largest emissions source identified in this study.

For purposes of this study, in most cases, the emissions were calculated fromonly those sources in which emissions were detected and/or could be measuredfollowing the procedures described . . .

. . . other sources of emissions, including but not limited to, storage tank breathingand standing losses, glycol dehydrator reboiler vents, wastewater and/orcondensate loading, and flaring were not calculated.25

I want to make it clear that I am not challenging any of these emissionsestimates. I know very little about emissions estimating. My onlypersonal interest in estimated emissions rates for industrial sources lies

in how these figures might be seen to relate to measured concentrationsof sulfur species on the ground.

Monitoring vs. modeling

My personal bias favoring measured concentration data over estimatedconcentrations reflects my own background as an air monitoringtechnician. Please accept my comments on this subject with this

admitted bias in mind.

The science of estimating emissions rates and modeling downwindimpacts is exceptionally complex, and I think the authors do an excellentjob of describing exactly how they did what they did in this section of thereport. There is little mystery as to how the researchers arrived at theirvarious calculations, as most of this is spelled out in detail.

The following excerpt is an example of how the data from just one samplewas integrated into the emissions estimates; and is provided here as an

example of just how complex some of this can get; and how carefully theauthors have explained their methodology.

1. The non-canister total organic compound emission rate was calculated by thenontank correlation equation. For the tee union with a % CFM of 0.39 the TOCemission rate was 11,644.25 lb/yr calculated as:

LR 2.3759*e * 0.39 11,644.25lbs /year 9.674501743 1.250318323 = = .Where:LR = TOC Leak Rate.2.3759 = SBCF


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9.674502= non-tank correlation equation intercept.26

Downwind impacts modeled

Yet another major undertaking of this project involved the

characterization of downwind impacts, and estimations of worst-casescenarios for concentration of various pollutants at facility fencelines;and at distances 200 and 600 ft beyond those fencelines.

In Table 5.3-1, on page 248 of the report, the authors compare theirmodeled predictions for some of the chemicals to the maximum levelsmeasured, and discuss possible explanations for some of the rather largediscrepancies in both directions. The reader is encouraged to view this

table.

In the following passage, the authors discuss the estimated

concentration figures for benzene and formaldehyde, both which wereestimated at levels higher than they were measured.

. . .the measured concentrations were intended to reflect some of the highest site-related air quality impacts; however, the monitoring generally did not occur atfence line locations, and the point source testing revealed that the ambient airmonitoring stations were not close to some of the highest-emitting well pads Thisdiscrepancy most likely explains why, for these two pollutants, the modeledconcentrations were considerably higher than the measured ones..

The study authors chose not to include a comparison of monitored vs.measured results for carbon disulfide, or to try to account for the largediscrepancies between their modeled worst-case scenario estimates andlevels of CS2 detected near NG activities in this, and other recentstudies.

Table 5.3-3. Modeled Annual Average Concentrations and TCEQ Long-Term Screening Levels27

Pollutant Highest EstimatedAnnualAverageConcentration atLocations 200 FeetBeyondFence Lines ppb

Lowest TCEQLong-TermHealth-Based ScreeningLevel

Type

Benzene 0.24 1.4 ESL

Carbon disulfide 0.00021 1 ESL


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Carbon tetrachloride 0.00096 2 ESL

Formaldehyde 4.34 2.7 ESL

. . . and H2S is not a Hazardous Air Pollutant.

In the point-source evaluation, emissions estimates are calculated forseveral categories of pollutants including Total Organic Compounds,(TOC) Volatile Organic Compounds, (VOC) and Hazardous Air Pollutants(HAP). The following definitions are provided:

TOC are the sum of non-VOCs and VOCs. VOCs are the sum of non-HAPVOCs and HAPs. Criteria pollutants are VOCs, particulate matter (PM), Oxidesof Nitrogen (NOx), Carbon Monoxide (CO), and sulfur dioxide (SO2). 28

I include this because I think this is an area where many people might

become confused. For the record:

Carbon disulfide and carbonyl sulfide are both VOCs (although onerarely sees carbonyl sulfide categorized in this way, or included in VOCmonitoring)

Carbon disulfide and carbonyl sulfide are both HAPs (in a big way,but neither are monitored here)

H2S is none of the above.

Hydrogen sulfide is an inorganic compound that is not identified by EPAas a Hazardous Air Pollutant under the Clean Air Acts of 1990, (CAA)although it remains quite deadly.29

Regulatory Analysis

A whole new ballgame now

On July 28, only two weeks after the release of the FWNGAQS final

report, EPA unveiled its long-awaited proposal for sweeping changes to

federal NSPS and NESHAPS30

rules governing oil drilling and the naturalgas industry. Because of this; analysis of federal regulations provided by

ERG in the FWNGAQS must now be viewed as pertaining only to theexisting rules, most of which will now become obsolete.

The regulatory analysis provided by ERG is presented as a generaloverview of potential issues raised by findings of the study, and was


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never intended to represent or include full-blown compliance audits atany of the visited facilities. This was all clearly communicated.

Due to the limited scope of the study, the authors were unable to makedeterminations regarding compliance status for many of the applicablesubsections of the state and federal rules.31 This subject is addressed insection 6.4 of the report; Regulatory Assessment Conclusions:

. . . For many of the rules potentially applicable to oil and gas sources in FortWorth, we were unable to make a definitive determination on whether the sourcewas subject to the rule, and/or whether the source was in compliance with therule. 32

Oh, Oh, Oh, Oh.

In their analysis of existing federal NSPS regulations, ERG explored theapplicability of two of the rules subparts: KKK and LLL.33

(Under the newly-proposed NSPS rules; these two subparts will beeliminated and replaced with subpart OOOO, in which EPA asserts broadnew regulatory authority under CAA. Many of the rules outlined insubpart OOOO involve previously unregulated NG production activities.)

The FWNGAQS authors found that site 159; the Crosstex AmineTreatment Centerwas potentially subject to Subpart KKKEquipment

Leaks of VOC from Onshore Natural Gas Processing Plants

This rule requires VOC leak detection and repair at facilities that remove naturalgas liquids from field gas. Site PS-159 (the Crosstex Amine Treatment Center)could be subject to this rule. However, status of compliance with the monitoringrequirements under this rule cannot be determined using the data obtained at thetime of the survey.

Our gas is not the sour gas

Because natural gas in the Barnett Shale is not considered to be sournatural gas none of the facilities in Fort Worth are identified as being

subject to Subpart LLLOnshore Natural Gas Processing: SO2Emissions

Sour natural gas is natural gas with an H2S concentration greater than 0.25 grainsper 100 standard cubic feet. The natural gas in the Barnett Shale is not consideredto be sour natural gas, so this rule does not appear to apply to any facilities in FortWorth.

The same language is echoed a few pages later in a section addressing


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the applicability of a TCEQ rule regarding the Control of Air Pollution fromSulfur Compounds. 34

Compliance with the ground-level concentration requirements under this rulecannot be determined using the data obtained at the time of the survey. As

mentioned previously, the natural gas in the Barnett Shale is not considered to besour natural gas, so this rule does not appear to apply to any facilities in FortWorth.

This part has always puzzled me. We are being told that gas sweetening

units in Fort Worth are exempt from regulation of sulfur emissionsbecause the gas they are sweetening was never considered to be sour in

the first place.

The authors do offer a clear definition of sour gas based on H2S content;

but do not provide any specifications for H2S in the feed gas entering theprocessing facility visited in the study, or provide any other explanationas to why any of the very nice gas in the Barnett Shale might ever evenhave to visit a place with a such a scary name as the Crosstex AmineTreatment Center.

Acid Gas Defined

On page 408 of the internet version of its proposed new regulations, EPA

offers the following definition of the term acid gas. 35

"Acid gas means a gas stream of hydrogen sulfide (H2S)

and carbon dioxide (CO2) that has been separated from

sour natural gas by a sweetening unit."

This easy-to-digest description of acid gas is consistent with informationregarding acid gas removal from natural gas streams publishedpreviously by EPA36; but the language here is so over-simplified as to be

dangerously misleading in my estimation.

Especially considering that this is being proposed as regulatorylanguage; this definition of acid gas - because it excludes the highlytoxic gases carbonyl sulfide and carbon disulfide - has the potential tobecome extremely problematic from a public health perspective.

These particular contaminants are known to be associated with theseparticular waste streams. These are highly toxic substances. Thesestreams are sometimes vented to atmosphere legally. I believe everyones


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interests will be better served by improved clarity and specificity fromEPA on this subject.

Meet the Pipeline Spec

In the natural gas industry, carbonyl sulfide and carbon disulfide aresometimes referred to as the sulfur acids, the organo-sulfur

compounds, or simply organic sulfur. Effective removal of thesecompounds from gas streams on a large scale requires specially designedfacilities which are extremely expensive both to build and to operate.

Efforts to develop more cost-effective treatment solutions for gas streamscontaining carbonyl sulfide and carbon disulfide have become a majorfocus for industry in recent years. This is true in natural gas processing;

and especially at domestic oil refineries, which increasingly rely on ready

supplies of inexpensive, high-sulfur crudes. Literature on this subject iswidely available in various trade publications and technical journals.37.38

The following information, including the table containing Typical GasPipeline Specificationsis lifted from the website ofQ.B. JohnsonManufacturing, Inc. According to information posted on the site, thisoutfit specializes in the planning, design and construction of gas

processing facilities to fit a wide variety of applications for clients in thenatural gas industry.

In addition to H2S and CO2, the sulfur acids, carbonyl sulfide (CS2), carbon

disulfide (COS) and the mercaptan family (RSH), when present in sufficient

quantities, are also candidates for removal with specific amines.

Typical Gas Pipeline Specifications: 39

H2S 0.25 grain/100 scf or 4 ppm

CO2 2-3 mol% (5% inerts)

CS2, COS, RSH 20 grains/100 scf

I have not been able to confirm any the information in this table, whichwas downloaded from http://www.qbjohnson.com . I am still activelyseeking information regarding these specifications. For my own

purposes, until I am able to locate reliable information to the contrary, Iwill assume that these figures are legitimate and not some type of hoax.

If the information presented in this table is accurate; and if pipelinespecifications allow for levels of carbon disulfide which are some 80x


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greater than those allowed for hydrogen sulfide, then I think this factmight help to explain some of the results of the recent air samplingsurveys in the FW area.

If this information does help to provide some answers though; at least inmy mind, it also raises these two immediate questions:

Why are we only talking about hydrogen sulfide in the sour gas

and acid gas streams? and

Why, in regards to carbon disulfide, do we just keep looking theother way?

Thank you very much for your attention in this matter. My name is

Andy Mechling. I live in rural southwestern Oregon. I have no affiliationof any kind. Opinions expressed have been my own. I can be reached at

[email protected] or (541) 660-8964.

I look forward to your questions or comments.

1City of Fort Worth Natural Gas Air Quality Study Final Report: 7.13.2011Eastern Research Group, Inc., Sage Environmental Consulting, LP.

2 I did pass a course Probability and Statistics as an undergraduate student atWhitman College in 1981. This was a challenging course. I think I got a C. I hold BAs inHistory and Communications.

3Table 5.2-3 Program-Average Concentrations and TCEQ Long-Term ScreeningLevels pp 241-245.

42.5.3 Key Pollutants p67.

55.2.2 Health Evaluation for Measured 24-Hour Average ConcentrationsComparing 24-hour average measurements to long-term health-based screening values

is scientifically inappropriate and is not done in this report. p232.

6 2.4 Quality Assurance/Quality Control, Table 2.4-1. pp35-36. Data QualityObjectives, Table 5.2-1. discussion pp226-227.

72.6 Ambient Air Monitoring Conclusions p90.

82.4.3 Measurement AccuracyAccuracy for the VOC and carbonyl analyses was established through audits that EPA

prepared and submitted to ERG as a regular function of the EPA National Air Toxics

Monitoring Program, which ERG manages and operates for EPA. p39.


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9Table 2.4-5. VOC and Carbonyl HAP Audit Results p39.

10City of Fort Worth Natural Gas Air Quality Study : Interim Ambient Air

Monitoring Report.2.11.2011Eastern Research Group, Inc. 7.1.1 VOCs p35.

11 Lower quality; not low quality. Test America / Austin produces high quality air datain this study; but in this study; their lab was clearly second best. The ERG lab

produces higher quality data, as is clearly documented in the report.

12This table was compiled by me utilizing information provided in Tables 2.5-4 through2.5-9 regarding Pollutant Study Averages pp50-62.

13Key findings from the ambient monitoring studyp90.

142.0 Ambient Air Monitoring p18.

155.2.1 Sensitivity of Monitoring Methods p226.

162.1.5 Site S-5 (High-Level Activity Site, Collocated)This sites location has a high level of natural gas activity and is within a mile ofdozens of natural gas wells upwind of this station. p26.

17Please notice that this figure reads ten parts-per-trillion. Here we finally gain accessto detailed information regarding ambient background levels of carbon disulfide in the

FW area. This is Urban Ambient Air - and thats Trillion with a T.

18Table 7-4: Pollutant CV Ratios at Each Monitoring Site Interim Report: p53.

19http://www.caslab.com

20Carbon Disulfide Method Development and Analytical Results for Kern CountyAir Monitoring Samples Collected in Six-liter Silco Canisters after Application of

Sodium Tetrathiocarbonate California Air Resources Board; December 2006.

21Toxicological Profile for Carbon Disulfide: 1996. Agency for Toxic SubstancesDisease Registry (ATSDR) EPA, CDC.

The monitoring data available for carbon disulfide are too limited to allow

adequate characterization of potential human exposure to the compound.

The biggest drawback in the existing studies is the lack of the ability to establish a

dose relationship between exposure and effect. More precise measurements of

exposure, control of exposure to other chemicals, and long-term follow-up of

occupational cohorts may lead to a better understanding of the dose-effect of carbon

disulfide.


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22Table 3.6-16. pp180-187

23Table 3.4-1:Comparison of Emissions Between Tank and Non-Tank Emission

Sources p117.

243.3.7 Canister Sampling. . . However, as Phase I testing commenced, it became apparent that thesampling teams were observing an unexpectedly high frequency of camera-detected emission points. Therefore, an alternative canister sampling strategy wasneeded; neither the project budget nor laboratory resources would be able to keepup with the canister demand. p107.

253.4 Emissions Calculation Procedures p113.

263.4.4 Applying Canister Results to Non-Canister Emission Points p118.

27Table 5.3-3: Modeled Annual Average Concentrations and TCEQ Long-TermScreening Levels p257.

283.5 Point Source Emissions Results p123.

29This compound did appear on EPAs original list of 190 HAPs, but was de-listed in thevery early 1990s by the agency; apparently at the request of then-president George

H.W. Bush.

30NSPS are New Source Performance Standards. NESHAP are National EmissionsStandards for Hazardous Air Pollutants.

316.1 Federal Air Quality Rules 6.2 p278, Texas Commission on Environmental

Quality Air Quality Rules p283.

326.4 Regulatory Assessment Conclusions p288.

336.1.3 New Source Performance Standards p279.

346.2.5 Control of Air Pollution from Sulfur Compounds p286.

35ENVIRONMENTAL PROTECTION AGENCY40 CFR Parts 60 and 63 RIN 2060-AP76

Standards of Performance for New Stationary Sources:

Oil and Natural Gas Production and Natural GasTransmission and Distribution; National Emission

Standards for Hazardous Air Pollutants From Oil and

Natural Gas Production Facilities;

and National Emission Standards for Hazardous Air

Pollutants From Natural Gas Transmission and StorageFacilities

60.5430 What definitions apply to this subpart?p408.


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36Acid Gas Removal Options for Minimizing Methane EmissionsLessons Learned from Natural Gas STAR Producers Technology Transfer Workshop

Long Beach, California August 21, 2007 epa.gov/gasstar

37 An Ace at Removal Olaf von Morstein, Johannes Menzel, Uhde GmbH, Germany and NagarajuPalla, Dennis Leppin, Gas Technology Institute, USA, discuss the first commercial application of a new

physical solvent for acid gas removal. (online article reprinted from Hydrocarbon Engineering

February 2004)

38The low-temperature hydrolysis of carbonyl sulfide and carbon disulfide:a reviewCatalysis Today, Volume 59, Issues 3-4, 25 June 2000, Pages 443-464Colin Rhodes, Stewart A.Riddel, John West, B. Peter Williams, Graham J. Hutchings

The impetus to reduce the emission of sulfur-containing compounds into theenvironment has become increasingly important in recent years. This paper reviews the

progress made towards reaching this goal and highlights the significant contributionsmade towards developing effective catalysts for the removal of carbonyl sulfide andcarbon disulfide. Novel promoter materials, new catalyst morphologies, new reactordesigns and developments for the future are reviewed and discussed.

39http://www.qbjohnson.com

Q. B. Johnson Manufacturing, Inc. can engineer, design and manufacture

treaters for any application. We have successfully provided treaters for

natural gas field installations, refinery off gas sweetening applications,

liquified ethane CO2 treating, raw NGL treating and others. If you have an

application requiring H2S, CO2 or any of the sulfur acids removal, please

contact . . .

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