Air Quality in the Barnett Shale - Part 28: Why Plot 2 used Carbonyl Disulfide

I was a bit curious as to why the FWLN Report sent to the FWISD included one model for carbon disulfide (Plot 1) and another model for carbonyl sulfide (Plot 2).  Everything up to this point had focused on the health concerns for carbon disulfide.

So I looked closer at the FWLN findings:

...and:

And then I looked at the statements printed on a green background in the report:

Okay...so it is all about the carbon disulfide.  So why produce Plot 2 for carbonyl sulfide?

Well duh!  Carbon disulfide was not detected by TO-15 in 46 out of 48 samples (see post) and ASTM Method D5504-08 detected carbon disulfide but had to qualify it as an artifact (see post).

But sample QLA5DC-1 did not have that inconvient qualifier:

So as I'm reading this and looking at the data, my mind is forming the question of; if there is no carbon disulfide detected in the BSEEC samples collected from different sites over different days, and carbon disulfide is the contaminant of concern, why spring carbonyl sulfide into the mix and continue to direct attention to carbon disulfide?

Doh!  Then it hit me.  FWLN is looking at carbonyl sulfide as a "byproduct" of carbon disulfide.  In other words, if you find carbonyl sulfide there must have been - or is - carbon disulfide!  Very astute FWLN!  Only you probably didn't figure on me checking into this, did you?

Yes, indeed, carbonyl sulfide is a "byproduct" of carbon disulfide.  It is produced when carbon disulfide is purposely manufactured.  Lets see what the EPA has to say on this:

You know what else the EPA has to say about carbonyl sulfide?

In the United States, the reported concentration of carbonyl sulfide in the air in rural areas was 0.27-0.80 microgram/m3.  Levels were 1.17 micrograms/m3 in Philadelphia, PA; 1.21 micrograms/m3 in Wallops Island, VA; and 1.37 micrograms/m3 in Lawton, OK.  Reported concentrations of carbonyl sulfide over salt marshes, which are major natural sources, range from about 60 to 180 micrograms/m3, and 14 to 19 micrograms/m3 over the ocean (HSDB 1994).

Well if I am going to be objective here, I need to follow this lead....

Okay...so finally we have something that indicates that we may have an issue with a contaminate in the Barnett Shale area above normally expected background.  And even if you subtract the maximum amount attributed to the artifact, in sample QLA5DC-1 you would still have 105 ug/m3.  That's more than comes off a salt marsh based on the EPA's research.

So lets work with this.  But first we need to make a few points clear.  First the presence of carbonyl sulfide in the ambient air samples collected has nothing to do with carbon disulfide.  And second, the non-detection of carbon disulfide in the BSEEC report using method TO-15 indicates that carbon disulfide is not present.

So the question I can reasonably ask now is carbonyl sulfide a concern? 

Now we are back to the one sample - low n's - issue.  However, carbonyl sulfide was detected above the artifact concentration of 25 ug/m3 in 6 of the 18 samples indicating a possible concentration above the levels found in an urban environment.  So lets assume that 130 ug/m3 (53 ppbv) is a valid number for carbonyl sulfide in the ambient air collected by BSEEC.

What does the BSEEC Report have to say about this:

Looks like the BSEEC folks got their units mixed up. This means that I need to check to see if the AMCV they report is in ppbv or ug/m3.  And guess what I find when I check?  There is no AMCV for carbonyl sulfide.  So where did "1800 ppbv" come from?

Well if I can find the acute ReV that would be the AMCV.  Search....nothing.  What about the RfC?  Checking the IRIS website....nothing, in fact they state:

The health effects data for carbonyl sulfide were reviewed by the U.S. EPA RfD/RfC Work Group and determined to be inadequate for the derivation of an inhalation RfC. The verification status for this chemical is currently not verifiable. No EPA documentation presently exists for this chemical.

Okay...so where did the BSEEC folks get a short-term AMCV of 1800 ppbv?  Well as of right now I have no idea.  I did find a short term ESL value that the TCEQ has derived in a 2008 memo:

So even at 130 ug/m3 (53 ppbv) the amount detected is well below the health-based ESL concentration of 540 ppbv which is 70% of the AMCV.....540 / 0.3...that equals 1800...hey...that's the AMCV the BSEEC folks reported!  

Okay, that gives us a value we can defend as health-based, assuming TCEQs POD and UFs are correct...they seem well supported.  And if the carbonyl sulfide ESL is listed for odor at 55 ppbm, it makes sense that the health-based threshold would be higher:

The short-term ESL is the lowest value of acute odor-, vegetation- and health-based ESLs. (Factsheet)

And at the highest carbonyl sulfide concentration detected - 53 ppbv - that amount is 10 times lower than the health-based ESL of 540 ppbv and more than 33 times lower than the ambient air concentration - the true health-based threshold - of 1800 ppbv.

Y'all double check my math (remember math makes my head hurt) to make sure I'm seeing this right....

Lab reports 53 ppbv...TCEQ states health-based ESL is 540 ppbv...at 540 ppbv the AMCV would be 1800 ppbv...okay...so the carbonyl sulfide in the Barnett Shale samples is well below health based levels.

So what does Dr. Sattler and the FWLN have to say about the carbonyl sulfide in their Report?

Huh?  How could the oil & gas source that produced sample QLA5DC-1 produce an emission rate that produces a model that that predicts concentrations one mile from the source that are "6 times greater than the health benchmark for carbonyl sulfide?"  At 1800 ppbv that would mean one mile out you would have concentrations at 10,800 ppbv?  Even if she incorrectly used the health-based ESL of 540 ppbv, that would show concentrations at 3,240 ppbv one mile from the source.

How is that physically even possible?

Maybe I'm missing something here, how can directly downwind from the source  - 50 -75 feet away - we find an actual concentration 130 ppbv but are able to get a concentration significantly higher further from the source?  How can the calculated emission rate from this actual value extend downwind one mile from the source at a concentration 6 times greater than what produced it at 50-75 feet away?  The same emission rate is being used, correct?  Doesn't Gaussian dispersion show the highest downwind concentrations nearest the source?

Wait a minute...Dr. Sattler is calculating an air concentration in and around the source (red area on her plot) of 655 ug/m3.  That's six times higher than the actual concentration detected within the red colored area around the source.  Now I'm really confused.  I mean the emission rate is staying constant, correct?  And the downwind concentration used to "back in" to obtain the emission rate is 130 ug/m3.  So with that "backed-in" emission rate, you would calculate 130 ug/m3 for the red area.  Yet in Plot 2, that area has a concentration of  655 ug/m3:

Okay...so lets assume Dr. Sattler's maximum 1 hour concentration for carbonyl sulfide is possible.  Would that maximum level pose a health-based concern?

• The highest concentration Dr. Sattler reports in Figure 1 is 655 ug/m3 or 267 ppbv.
• The maximum concentration of 267 ppbv is less than the ESL of  540 ppbv.
• 267 ppbv is less than one half the amount of the health based ESL
• 267 ppbv is less than six times the health based ambient air concentration of the AMCV.

So why would Dr. Sattler and the FWLN insist that the concentrations one mile from the source could be as high as "6 times the health benchmark for carbonyl sulfide?"  Well lets look at Dr. Sattler's Report on Plot 2 to see what's up about this:

The 1-hour Texas Commission on Environmental Quality (TCEQ) Effects Screening Level (ESL) for carbonyl sulfide is 135 µg/m3; one of the sample concentrations exceeded this level.

.... ah...that's why!  Dr. Sattler is using an odor ESL threshold for the "health benchmark" that is being exceeded:

...and if you will recall, "The short-term ESL is the lowest value of acute odor-, vegetation- and health-based ESLs."

So even if Dr. Sattler's model is correct, the carbonyl sulfide in Plot 2 does not pose and adverse health risk.

And if that is true...and the fact that 46 our of 48 BSEEC TO-15 samples showed non-detect for carbon disulfide, and the two samples that were positive were less than 0.3 ppbv... then there is no health based concern for carbon disulfide or for carbonyl sulfide and the requirement to have a one-mile setback based on the health concerns for these two contaminants is not warranted or substantiated by any of the data provided in the FWLN or BSEEC or ERG reports.

And just so we are clear on this.  The need to provide - or not provide - a setback for O&G operations is not being argued here.  The basis for a one mile setback recommendation due to health-based concerns regarding carbon disulfide and/or carbonyl sulfide is.

And that's all I can really say about this....

Next Post: Air Quality in the Barnett Shale - Part 29: Where should we go from here?

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Air Quality in the Barnett Shale - Part 18: Dr. Sattler's Deposition - 70% means what?

For the last four posts I've been looking at how Alisa Rich with Wolf Eagle Environmental and Dr. Sattler with UTA could have concluded that the results of air dispersion modeling performed on six ambient air samples collected over a 24-hour period indicated a problem with the air the good people of the Town of Dish, Texas, were having to breath now that a bunch of gas compressors were located in their town.

I've been critical of their work on many fronts, but it all seems to revolve around the use of ESLs to compare ambient air samples.  This is not what ESLs are to be used for, but Alisa Rich, with the assistance of Dr. Sattler, decided that it would be appropriate to use them in their reports.

The two of them have been unable to get their heads wrapped around why the ESL shouldn't be used, going so far as to accuse the TCEQ of not being technically competent when they tried to rectify this misuse with the issuance of the AMCV for ambient air samples, like the ones collected by Alisa Rich.

In their thinking, a value that is 70% lower than another must be, somehow, more safe.

So is the ESL that is 70% lower than this new AMCV value the TCEQ wants to use a better value to use?

No.


ESLs and AMCVs are based on an inhalation Reference Value (ReV) which is defined:

[a]s an estimate of an inhalation exposure concentration for a given duration to the human population (including susceptible subgroups) that is likely to be without an appreciable risk of adverse effects. ReVs are based on the most sensitive adverse health effect relevant for humans reported in the literature.

For non-cancer causing chemicals and chemicals that show a nonlinear effect, the formula:

• (acute)ESL = 0.3 x (acute)ReV
• (chronic)ESL = 0.3 x (chronic)ReV
• (acute)AMCV = (acute)ReV
• (chronic)AMCV = (chronic)ReV

For chemicals suspected to cause cancer the ESL and AMCV are the same.

The ESL is one third the ReV.  And the ReV is the value which is based on the most sensitive adverse health effects relevant for humans.

So if the AMCV = the ReV, and the ReV is the value which is based on the most sensitive adverse health effects relevant for humans, will lowering the value by 70% bring about any more protection?

No.

Another way to look at it is like this:  If the maximum temperature that a hot tub will go is 104F, is 104F the maximum temperature deemed safe for humans?

Yes.

If we lower the temperature to 90F, will we have made it any more safer?  How about to 65F?

No.

Now the thing about temperature is this.  If you add 90F water to 90F water, the water will be 90F.  But if you add 60 ppb of Benzene from one source with 60 ppb of Benzene from another source, you could get 120 ppb of Benzene in the ambient air.

If the ESL for Benzene is 54 ppb, the two sources would be putting more Benzene into the air than they should, but it would still be at a safe level.  Even when the two concentrations are added together (120 ppb) it is still safe because 120 is less than the ReV which is 180 ppb.

And you know what the AMCV for short term Benzene is?  180 ppb.

Since Benzene is also a suspected carcinogen, the long-term (chronic) level is set to 1.4 ppb for an average over a lifetime for both the ESL and the AMCV.

So there you have it.  You could be exposed to 180 ppb for up to one hour with no adverse health effects and as long as your average (for a lifetime) does not exceed 1.4 ppb, you should have no adverse health effects from Benzene.

That's how it works.

Now go check the TCEQ's ambient air monitoring web site to see what the one-hour levels for Benzene are. (make sure to check; measured in ppb-v, clear all checkboxes, check benzene, generate report)

I'll wait.

See?  Feel better now?

So just so we are clear on this.  The AMCV is the ReV.  The ReV is based on the most sensitive adverse health effect relevant for humans reported in the literature.  The ESL is 70% lower than the AMCV.

Next Post: Air Quality in the Barnett Shale - Part 19: Dr. Sattler's Deposition - Down with bad science!

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Air Quality in the Barnett Shale - Part 17: Dr. Sattler's Deposition - TCEQ Competency

For the last few posts I have been commenting on the Deposition of Dr. Melanie Sattler in the lawsuit of Law v. Range Resources.  My posts deal with the Town of Dish, Texas, which involve work done by Dr. Sattler and Alisa Rich of Wolf Eagle Environmental.

Now it may appear that, like the defendant's lawyer, I am trying to embarrass Dr. Sattler or ridicule Alisa Rich.  That's not the purpose of why I am writing this.  My goal is to show how and where their thinking is wrong, misguided, or has become biased.  I hold everyone accountable for supporting their beliefs and comments, but I especially hold someone with a MPH, as well as anyone who teaches, with a higher level of accountability.  Bad science leads to bad decisions.

What these two professionals have put forth as "based on reasonable scientific probability" is anything but.  And it all relates back to their complete lack of understanding of a risk based exposure level (AMCV) and a contaminant level designed to allow for future growth (ESL).  All of this - plus a hefty dose of mistrust in the TCEQ - has lead these two down a path of paralogism.

I find it intellectually dishonest to discuss something - especially teach it or use it as the basis of a report to the general public - without attempting to understand it fully.  I had no idea what an ESL or AMCV was before I read Alisa Rich's reports to the Town of Dish, Texas.  I have the same degree as Alisa Rich so we should have come up with the same understanding.  Dr. Sattler is a Ph.D dealing with ESLs.  She should understand them fully, or at the very least be able to see how it is illogical to even contemplate a health concern if the value was ".001 micrograms per metered cubed above that."

So lets look at how these two look at the ESL and the AMCV:

Q. What is your understanding of an Effects Screening Level [ESL]?

A. They are used for comparison of dispersion modeling concentrations to assess whether there could be a potential short-term or long-term health impact.

Q. And the [ESL] are used for permitting purposes; are they not?

A. That's correct.

Q, [T]hey are not ambient air concentration levels, or shouldn't be used to compare ambient air concentration levels should they?

A. They have been used that way in the past, until recently when TCEQ came out with the [AMCV], [b]ut they have come out with a new set of values that they say are appropriate to compare ambient measurements with, but the {ESL] are still the appropriate values for comparing dispersion modeling results with.

It was at this point that I started to realize that Dr. Satller did not understand the difference between using a dispersion model to predict health impacts to a receptor and using an ambient air sample to conclude possible health impacts.  What was happening here is comparing apples to oranges.  Even though an ESL looks at health impact to a receptor, when Alisa Rich placed the canister to collect the sample, she was collecting an ambient air sample.

ESLs have never been appropriate for looking at potential health impacts for an ambient air sample since they are designed for permitting purposes.  They are purposely made to be 70% more protective than what is actually required.  This is why the the TCEQ brought forward the Air Monitoring Comparison Value.  Dr. Satller was aware of this, but possibly did not understand what the 70% decrease actually means.

A. The TCEQ Guidance says that the [ESL] are appropriate values to use for dispersion modeling because when your doing dispersion modeling, typically you're looking at the impacts of one source.  And so the [ESL] are set lower in some cases than the [AMCV] to allow for, like, future additional sources that might move into the area that arn't accounted for in the dispersion modeling.

So you don't want one source taking up all of the air quality, [a]ll of the room in the atmosphere for emissions of that compound, because there may be future sources that move into the area that may also emit the compound.  So in some cases the ESLs are set lower than the [AMCVs].

Dr. Sattler sees it, articulates it, but does not understand it.  If the ESLs are set lower to accommodate growth, then exceeding them would not indicate a health concern, since they are designed to allow another facility into the area that would emit up to a similar amount. 

Simply put; if source A puts 2 ppb into the air, and a new source, B, puts 2 ppb into the air, than the total ppb in the ambient air would be 4 ppb.  If the ESL is 2, then it is OK for both A & B to put that amount into the air.  So if this is OK, then how should one look at the 4 ppb actually now in the air?  That's why they developed the AMCV, because the ESL is appropriate for only one source in an area and is used only for air permitting - to see what additional air pollution devices or setback may be necessary for that one source.  The dispersion modeling looks to make sure that a receptor in and around that source will not be exposed to more than the ESL form that source.

If an ambient air sample - like Alisa Rich took in the Town of Dish, Texas - has levels above the ESL, it does not indicate a health concern since the ESL is 70% lower than what is considered to be a safe level.

So, when Alisa Rich and Wilma Subra reported that the ambient levels exceeded the ESL, they were incorrect.  When Dr. Sattler produced modeling results that showed receptor concentrations above the ESL, she erred not only in how the source's emission rate was calculated but in her data's ability to now allow Alisa Rich the means whereby she could allude that there was a health issue in the Town of Dish, Texas.  Her report under "Results" states:

"The basis of an ESL is health impacts..." and "According to Table 2, short-term and long-term ESLs were exceeded for all pollutants, with the exception of long-term ESLs for styrene and toluene."

Now it is my belief that Alsia Rich knew full well how Table 2 would be interpreted by the people in the Town of DISH, Texas, as well as anyone who has a concern about oil & gas production.  All her reports are written in such a way as to not make a conclusion of yes or no, but instead are cleverly worded to be truthful without being honest.  She must - as an MPH - understand how the ESL is calculated, as should Dr. Sattler.  However, Dr. Sattler's lack of a toxicological background may preclude her understanding of Hazard Quotient (HQ) and Cancer Slope factor (see  1.6.1.1 Calculation of ESLs for Nonlinear Effects)  which might account for why she has continued down this path and, unfortunately, brought her students along with her.

To know what the model is designed to do, but completely lack an understanding of what the numbers produced mean, is just....well I don't know what to make of it.  I think the idea behind Alisa Rich's dissertation is sound - that the ratio of chemicals detected in the air might be used to determine the possible source - has potential merit.  But using the model to back in data without this fingerprinting knowledge - which was done in all three studies provided to Alisa Rich - is unsound, making all this modeling work performed by Dr. Sattler nothing more than guessing.  At the very least I will accuse her of being intellectually sloppy in her premise and her understanding of what the true health impact should be identified as.

They don't hand Ph.Ds out to just anyone, so when you have that, along with the title of "engineer" and "professor" at a "major university" by your name, it is assumed that you should have a pretty good understanding of what your are saying.  It assumes that you have spent the time necessary to thoroughly research your topic, to know it inside and out.  If her topic is air dispersion modeling, then one should reasonably expect that she fully understands what the number the model calculates means.  She doesn't, and how many people has she confused because of her failure to look at anything other than the number produced?

Numbers mean something.  The air dispersion model numbers mean something.  They are used to compare against an ESL.  She knows that.  So how in the world does she not understand what an ESL is all about?

Q. [Your 6/15/10 email states] "It seems like the TCEQ should have been using AMCVs all along as a basis of comparison for monitoring data." [S]o if someone was taking ambient air tests certainly after June of 2010, the intellectually honest thing to do would be to compare that data to AMCVs, not [ESLs] correct?

A. In my opinion.  There are people who suspect the motives of the TCEQ in issuing the AMCVs at this late date; why didn't they issue AMCVs 20 years ago?

Q. [t]he intellectually honest thing to do if you're taking air data from ambient air samples would be to compare it to that, not [ESLs] which are set 70 percent lower than the level at which health effects would be anticipated; correct?

A. I don't think the issue is that simple, because, as I said, if AMCVs were the proper thing to use, why didn't TCEQ come out with them 30 years ago.  So there are people that suspect the TCEQ's motives in issuing the AMCVs.  And if you're one of those people, you can argue that it's appropriate to go ahead and continue using the ESLs as we have - as they have been used in the past 20 years or whenever it was that they first came out with the ESLs

I'm going to interject here.  The reason they had to put the AMCVs in place is because of Alisa Rich and Dr. Sattler's misuse of them.  Prior to Alisa Rich's "reports," they were used for air permitting, not for ambient air determination of a potential problem or concern.  Alisa Rich and Wilma Subra took ambient air samples and compared those values to values that are 70% lower than what is consider to be health based.  Then, to top it off, Dr. Sattler "backs in" this ambient air data into her dispersion model and calculates potential concentrations that are, once again, compared to ESLs.  This causes the people in these communities and those around oil & gas production sites to believe that they are being harmed.  Their (TCEQ) motive was to stop this abuse/misuse.

Oh, but it gets better...so unbelievably better:

Q. Are you one of the people that suspects the TCEQ's motives?

A. I don't know.  I've worked with some people at TCEQ that are technically competent, and I've worked with some people that arn't as technically competent, so I hope that the technically competent people were involved in this decision, but I don't know for sure.

Q. When you said [i]ts reasoning seems OK," have you changed your mind about that since June 15, 2010, as you sit here today?

A: If I read the document and take it at face value, the document seems okay, but there have been some other - decisions that TCEQ has made that I think have not been technically sound since that time.

Q. Do you [h]ave any reason to think that Alisa Rich questions the motives of the TCEQ?

A. Yeah

Q. And what do you base that on?

A. Because she's been reluctant to start using the AMCVs as a basis of comparison.

Q. And why is she reluctant to use the AMCVs as a basis for comparison?

A. Because we've been using [ESLs] to compare monitoring data for the last 20, 30 years, however long the ESLs have been in existence, and so I think she questions why - why they're just now coming up with them; why didn't they come up with them 20, 30 years ago.

So maybe I was wrong to assume that Alisa Rich - who holds an MPH, like me; from a reputable University, like me; with a focus on environmental health, like me - should understand why the ESL was replaced by the AMCV for ambient air monitoring.  It's all about the HQ and the Cancer Slope Factor, the BASIC principle behind assigning risk.  The TCEQ ESL document explains it all very well.

Air dispersion modeling is all about looking at risk.  To not understand the difference between the ESL and the AMCV, is to not understand the very basis of how we look at potential adverse health effects from one source and all sources combined

Q. If you were doing an ambient air study [w]ould you use the AMCVs as the comparison value as opposed to the ESLs?

A. Yes

Q. And you would do that because you believe that would be the intellectually honest thing to do; correct?

A It would be because I would take the AMCV report at face value and - hope that the people who decided to come up with the AMCV standards were the people at TCEQ that were technically competent.

And the TCEQ, environmental professionals like me, and the general public at large, would hope that someone with a Ph.D, a job as a UTA professor, and an engineer in air dispersion modeling, would be technically competent to be able to determine this on her own and not just reluctantly accept it at "face value."

AMCVs are the correct level to use when looking at ambient air concentrations.  ESLs are used to look at what level a receptor would be exposed to if the emission rate from the source is known.  ESLs are 70% less than AMCVs because they are used for permitting.  Exceeding them does not indicate a health concern.


Next Post: Air Quality in the Barnett Shale - Part 18: Dr. Sattler's Deposition - 70% means what?


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Air Quality in the Barnett Shale - Part 16: Dr. Sattler's Deposition - Those Seven Chemicals

In the Wolf Eagle Environmental report for the Town of Dish, Texas, Alisa Rich used values produced from dispersion modeling performed by Dr. Sattler of UTA.  These values are listed in Table 2:

Dr. Sattler's dispersion modeling maximum concentrations were developed using sampling data - collected with six SUMMA canisters possitioned a distance away from the oil & gas production site - provided by Alisa Rich.  Of these seven chemicals, two (Benzene and Toulene) are part of BTEX which is a common air pollutant derved from burring fossel fuel and cigaretts.  According to the EPA:

The primary HAP associated with the oil and natural gas production and natural gas transmission and storage source categories include BTEX and n-hexane. In addition, available information indicates that 2,2,4-trimethylpentane (iso-octane), formaldehyde, acetaldehyde, naphthalene, and ethylene glycol may be present in certain process and emission streams. Carbon disulfide (CS2), carbonyl sulfide (COS), and BTEX may also be present in the tail gas streams from amine treating and sulfur recovery units.

The State of New York identifies 1,2,4-Trimethylbenzene as a "chemical constituent" of "chemical additives proposed to be used in New York for hydraulic fracturing operations at shale wells."

This leaves styrene and dimethyl disulfide without a recognized association with oil & gas production.  Since these two chemicals were detected Alisa Rich and Dr. Sattler assume they must have come from the oil & gas production site in question and build a dispersion model as if they did.  This is why you can't back in air sample contaminant levels taken some distance from the source without first understanding what the normal background level is for the chemicals in question. There is no reason why styrene or dimethyl disulfide would be coming from this site.  Since styrene is a HAP, it would have been identified as chemicals of concern for oil & gas production MACT/GACT compliance under NESHAPS.

So lets say those two chemicals are background contaminants that came from some other process unrelated to oil & gas.  That leaves five remaining.  Both carbon disulfide and carbonyl sulfide (as well as dimethyl disulfide) were identified in the final report and in the lab reports as Tentatively Identified Compound (TICs).

This creates a bit of a problem that was not addressed in the report.  Here is what the TCEQ has to say about TICs:

TICs are observed measurements in the sample for which the gas chromatograph-mass spectrometer (GC/MS) was not specifically calibrated; however, the tentative identification of a compound can be made by comparing the mass spectrum from the environmental sample to a computerized library of mass spectra. The comparison of the sample spectra and that of the library are scored for their similarity to the mass spectrum of a particular TIC and the tentative identification is made based on the most similar spectra. This is a commonly used technique; however, the absolute identity of a TIC is uncertain. Quantifying TICs is also less accurate than for target compounds because the true relative response factor is not known, since the instrument was not calibrated for the TIC. It is important to note these uncertainties when evaluating TICs.

Given the uncertainties in identification and quantification of these compounds and the method used to determine potential 1-hour maximum concentrations, it is not possible to accurately draw conclusions about the potential for adverse health effects.

I understood why, but not to the level needed to discuss it here.  So I asked my professor over at SRPH that happens to know a little bit about analysis and GC/MS.  "It's because of the response factor" he said.  I just nodded my head making a mental note to Google that when I got back to my office.  Here is what I found to be a pretty good explanation of a Response Factor:

The size of a spectral peak is proportional to the amount of the substance that reaches the detector in the GC instrument. No detector responds equally to different compounds. Results using one detector will probably differ from results obtained using another detector. Therefore, comparing analytical results to tabulated experimental data using a different detector does not provide a reliable identification of the specimen.

A “response factor” must be calculated for each substance with a particular detector. A response factor is obtained experimentally by analyzing a known quantity of the substance into the GC instrument and measuring the area of the relevant peak. The experimental conditions (temperature, pressure, carrier gas flow rate) must be identical to those used to analyze the specimen. The response factor equals the area of the spectral peak divided by the weight or volume of the substance injected. If the technician applies the proper technique, of running a standard sample before and after running the specimen, determining a response factor is not necessary.

"Basically," he said.  "Because you did not use a standard that included these TICs, the computer makes a guess as to what chemical the peaks could represent."  He then showed me how this works by letting the computer identify an unknown bunch of peaks on a spectra he had.  The computer spat out a name.  "The lab tech needs to look at the peaks and compare it to the peaks of the compound the computer picked out.  If it's a match, great, but a lot of the time, like this example, the computer gets it wrong."

So basically what he showed me was the analytical equivalent of Damn you Auto Correct.   But they quantified these chemicals I said.  He just stared at me and then shook imaginary dice in his hands and let them fall.  I got the message.  Even if you spent the time comparing the peaks to the chemicals in the library, the lack of a standard means the quantity reported is nothing more than a guess.  Which is why the TCEQ says:

Given the uncertainties in identification and quantification of these compounds and the method used to determine potential 1-hour maximum concentrations, it is not possible to accurately draw conclusions about the potential for adverse health effects.

Well I called the lab and asked them if they physically compared the peaks found to the chemical in the library that the computer picked up.  They said no.  Damn you auto correct!

Now, to be scientific about this - which Alisa Rich should be and Dr. Sattler must be - with this information, we really need to exclude styrene, dimethyl disulfide, carbon disulfide, and carbonyl sulfide from the model.

That leaves only Benzene, Toluene, and 1,2,4-Trimethylbenzene with any reasonable plausibility for being emitted from the oil & gas production site.  Lets look at this from both a comparison to the ESL and AMCV.

Note: Toluene AMCV is for health.  ug/m3 were converted to ppbv using the formula 24.45 x concentration (ug/m3) ÷ molecular weight.  

When compared to the AMCV - which is proper in this case, and any case where air pollution permitting is not the goal -only Benzene and 1,2,4 Trimethylbenzene exceed the Annual AMCV based on the premise that these two chemicals came solely from one source only - the oil & gas production site.

So looking at it under these conditions - straightforward, fair, scientific based - what is the conclusion for the air in the Town of Dish, Texas even if these values were backed in the model?  Remember, those values reported in Table 2 are worst case possibilities.


Next Post: Air Quality in the Barnett Shale - Part 17: Dr. Sattler's Deposition - TCEQ Competency


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Air Quality in the Barnett Shale - Part 7: Benzene Exposure and the No Significant Risk Level.

Carcinogens are a bit trickier to deal with in terms of determining a safe level.  This is because there is no concentration other than zero that one can say will present no chance of getting cancer from exposure to it.  Instead of a threshold dose, we look at a exposure level determined to present "no significant risk."

This level is defined as the level which is calculated to result in not more than one excess case of cancer in 100,000 individuals exposed over a 70-year lifetime. In other words, if you are exposed to the chemical in question at this level every day for 70 years, theoretically it will increase your chances of getting cancer by no more than 1 case in 100,000 individuals so exposed. (5)

What it does not mean is that one person per 100,000 individuals will get cancer.  This is the same concept behind rolling a six sided die.  You expect to see a "one" show up every six rolls, but you could roll it 50 times without ever rolling a one.

Basically, the ESL and AMCV are calculated the same way:

• (chronic)ESL = 0.00001 / URF
• (chronic)AMCV = 0.00001 / URF

The URF or "Unit Risk Factor" for carcinogens do not have a threshold dose at which below that concentration no cancer would take place. What this means is that any exposure has the chance to cause cancer and that the more exposures the more chances for cancer to manifest itself result.  This makes exposure to "Benzene, a know human cancer causing agent" a scary thing to read over and over again in a report (7).  This is where context and explanation are critical components to any report involving a complex formula, a number, and the words "know human cancer causing agent."  This is also where Alisa Rich, who - need I remind you again - has a Master in Public Health, failed to convey the risk properly.

Why did Alisa Rich and Wilma Subra fail to put this information in context?  Maybe it's because they lack a basic understanding of how the "no significant risk" is calculated and how to compare the 24 hour values with this risk.  It is quite possible that we receive a much better education in our MPH program at Texas A&M's School of Rural Public Health than one receives at the University of  North Texas, but I know that is not the case here.  So instead I will assume that both of  these experts just don't fully understand the topic they sell themselves as knowledgeable in.

Here is how TCEQ explains it in their 2006 document called "Guidelines to Develop Effects Screening Levels, Reference Values, and Unit Risk Factors" in 1.5.2:

For adverse effects associated with a linear dose-response [such as carcinogens], it is assumed that an effects threshold does not exist. Therefore, a linear extrapolation from the POD [point of departure] to the origin of the inhalation dose-response curve is performed to estimate excess lifetime risk at lower doses. The slope of the line from this linear extrapolation is the inhalation URF, which is defined as the upper-bound excess risk estimated to result from continuous lifetime exposure to an agent at a concentration of 1 μg/m3 in air (i.e., risk estimate per μg/m3). 

Confusing?  Lets look at this in terms of Benzene: (8)

• EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated a range of 2.2 x 10-6 to 7.8 x 10-6 as the increase in the lifetime risk of an individual who is continuously exposed to 1 µg/m3 of benzene in the air over their lifetime.  
• EPA estimates that, if an individual were to continuously breathe air containing benzene at an average of 0.13 to 0.45 µg/m3 over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of continuously breathing air containing this chemical.
• Similarly, EPA estimates that continuously breathing air containing 1.3 to 4.5 µg/m3 would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 13 to 45 µg/m3 would result in not greater than a one-in-ten thousand increased chance of developing cancer.

So the Benzene values obtained from a single 24 hour sampling event performed by Wolf Eagle Environmental were

Now on first glance, one might think "I'm going to get cancer because of Samples 2, 3,and 4."  But that is not the case.  There are two things necessary for one to develop cancer from breathing this particular air.  The first is you would need to breath that air - at the concentration - for 70 years.  Secondly, your body would have to have develop a cancer from the uptake of that particular contaminant.  

It's a lot like flipping a coin.  If you have a 50% chance of the coin landing on tails - when you flip the coin - either heads or tails can come up.  So if I told you you had a 1 in 2 increased chance in developing cancer, you might not want to be exposed.  Now lets change that coin for a single die with six sides.  If you exceed that level over a lifetime, you roll the die and if the number "one" shows up you get cancer.  That would be a one in six increased lifetime chance.  Now lets change out that 6-sided die for one of those funky die they use when playing Dungeons and  Dragons, only in this case, it will have 100,000 sides to it with the numbers 1 to 100,000.  Now if you continuously breath air containing 1.3 to 4.5 µg/m3 of Benzene for a lifetime, you would roll this 100,000 sided die and if the number "1" came up you would get cancer.

For samples 2, 3, and 4, the benzene level is higher than the amount deemed no significant risk.  In this case, the risk - if one were to be exposed at that level in sample 4 constantly over a 70 year lifetime-  would be between:

• 247.9 x  0.0000022 = 0.0005   and    247.9 x 0.0000078 =  0.002

Or an added - or excess - lifetime risk between 1 in 500 and 1 in 2000.  At these elevated levels, the cancer risk has increased, but that is only if the exposure remains at 247.9 ug/m3 and the body fails to repair itself and develops a cancer.  Obviously the levels of benzene detected are too high and additional investigation should be done to determine the cause and fix the problem.  But even at these levels, cancer from benzene is not inevitable.

So looking at this in context, exposure to benzene has the potential to cause cancer but unless the levels are high and sustained over a lifetime, the risk of cancer is not significant.  You may be the unlucky person that rolls the "1".  This is where evaluating risk comes into play and the concept of accepted risk and risk that is forced upon you.  One may reasonably conclude that any risk is a risk too many.  But is eliminating the potential for a one in 100,000 possibility at something negative happening worth the benefits obtained from having it?  I can't make this decision for someone who is potentially impacted by the risk coming from those benefits.  What I can do is try and put it in perspective.   Because even if you eliminated every gas well and drilling rig from the area, exposure to Benzene will still take place and cancer - from lots of other sources - will still manifest itself.

There are a lot of factors in place for citizens in and around gas production activities.  The fact that we find chemicals in the air on one particular day does not mean that exposure at that level will take place the other 364.  And even if there is exposure at that level, we still do not know if the second to final step in the K. C. Donnelly Risk Paradigm - uptake - takes place.  And even if uptake does happen, the body is very good at dealing with contaminants through a process called pharmacokinetics.  And even if we end up with a negative health effect we have very good medical procedures to treat this.

And even if the die rolls a one, we are still unable to pinpoint the culprit, for we have no background data on what levels of these contaminants were present before the gas operation began.  All of this must be taken into consideration befor you say "yes" or "no" to assuming the risk.

Now lest you think I am giving the oil and gas industry a free ride here, I am not.  I will deal with their issues at the conclusion.  What I am writing about in these posts is how Wolf Eagle Environmental and Wilma Subra have painted a picture that does not represent fully and accurately the reality the citizens of the Town of DISH Texas are facing.  That is unfair to them, unfair to the Oil & Gas industry, and unfair and damaging to my profession which is dedicated to protecting the environmental and public health.

Next post: Air Quality in the Barnett Shale - Part 8: Benzene is like a bull...

Note: 2/16/11 A bio found on the internet lead me to incorrectly assume that Alisa Rich received her MPH and was working on her Ph.D from UT.  An email I received from Barnett Shale News included a Deposition from her stating she got her MPH from UNT's Health Science Center and is working on her Ph.D at UT Arlington.
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Air Quality in the Barnett Shale - Part 6: Cumulative Risk & ESL Development

In my last post, I wrote that the TCEQ, makes a rather unambiguous statement regarding the health concerns in the Barnett Shale stating explicitly:

"[T]here are no immediate health concerns from air quality in the area."

Now you can read into that what you will.  You can ignore it, you can disagree with it, you can doubt it, or you can follow up with, 'but what about long-term health concerns?' For which the TCEQ addresses by stating:

"[T]hat when they are properly managed and maintained, oil and gas operations do not cause harmful excess air emissions.”

There are two issues I am trying to address with these posts.  The first is Wolf Eagle Environmental assertion that the chemicals present pose an acute and/or physical hazard:

While atmospheric Methane concentrations recorded over the past year in the Town of Dish do not exceed TCEQ ESLs, the intrinsic quality of Methane to be an asphyxiant should not be overlooked.  In addition, Methanes is highly flammable and can form explosive mixtures in high concntrations in air." (1)

"In addition, several locations confirmed exceedences in a chemical identified by TCEQ with the capability for 'disaster potential'," (2)

The second asks the question does exposure to these chemicals at the levels detected in the one hour and annual averaging - as well as the levels reported by Wolf Eagle Environmental pose a chronic health concern?  That's the $64k question, since some adverse health effects take decades to manifest themselves.  So what toxicologists and health officials do is try to determine a "safe" level.  Unfortunately we are exposed to many chemicals at different concentrations throughout the day and over our lifetime.  Because two or more chemicals can interact synergistically, additively, antagonistically, or be potentiating, a cumulative risk approach is adopted.

In the process of determining risk and/or a 'safe' level, the culprit releasing the chemical of concern is not important.  So when ambient air monitoring is performed it takes a snapshot of all the different chemicals that were present in the air at the one location in time.  What has been shown is that single chemical contaminants can be detected intermittently over time and a single chemical detected at that one location may come from multiple sources. (3)

TCEQs ESLs are "intended to be comparison levels used in the TCEQ’s air permitting process to help ensure that authorized emissions of air contaminants do not cause or contribute to a condition of air pollution."  ESLs are used for air permitting whereas the “air monitoring comparison values” or AMCVs are used for comparing air monitoring results.  ESLs are chemical specific concentrations modeled on a worst-case ground-level air concentration of a single chemical exposure and the potential for an adverse effect due to operation of the facility.  ESLs are very conservative in how they are calculated so when a measured concentration is above the ESL, a review of the actual toxicity data on that chemical may conclude that health effects would not be likely to occur at that level. ((AMCV Document))

Say what?!?  Yeah...which is why the TCEQ goes on to say:

"This broad conservative application of the ESLs has resulted in misunderstandings among the public because the ESLs did not represent the predictive toxicity of the chemical. ESLs continue to be useful screening values for air permitting, but more realistic, predictive values are needed for use in the review of ambient air monitoring data."

Why would they do this?  Why would the purposely develop a method that - for the most part - says - It is a health problem if it exceeds the level unless it isn't a health problem.  That's what Dr. Robin Autenrieth meant when she said "the people demand a number."

Because chemicals do not follow the same drummer, coming up with a uniform way to categorize their toxicological health risk - the "number" we can compare to - creates situations where on one hand it exceeds the level that indicates a health risk but on the other hand there is no data showing a health risk at that level.

And we wonder why the public can be confused, and - in the case of data presented by two experts - misled to believe there are problems because of the number of times a contaminant exceeded this level.  And if I have not beat this dead horse enough, it is inexcusable for Alisa Rich - who holds a Master in Public Health from the University of Texas - to not have understood this and addressed it accordingly in her reports to the good people in the Town of DISH, Texas.

But I digress.  So if the people demand a number, how is this number derived?  Well it basically boils down to this - "the no significant risk level for an individual chemical" defined as:

• the concentration associated with a hazard quotient (HQ) of 1, and...
• the concentration associated with a theoretical excess lifetime cancer risk of one in 100,000 (1 x 10-5).

This where the math that is needed to derive the number comes into play.  Mathematics follow very hard and fast rules.  Two plus two always equals four.  But in toxicology, there are very few hard and fast rules.  Almost everyone has heard stories of someone who drinks like a fish and/or smokes like a chimney and lives to be 90!

So to level the playing field as to what is 'safe' the HQ is used for concentrations of non-cancer chemicals and the theoretical excess lifetime cancer risk of one in 100,000 is used for cancer causing chemicals.  Because there is both cumulative and aggregate exposure to chemicals, the TCEQ uses an HQ of 0.3 to calculate Short-term and Long-term ESLs for the bulk of chemicals.  This is why an ESL is described as "70% lower than the reference value" itself. (6)  In most risk assessments, the HQ is set at "1" which is how the AMCV is calculated.

Why the difference for air permitting and air monitoring?  I am not quite sure, what I suspect is that air monitoring assumes a baseline amount - that is - there is nothing that can be done about that concentration we are exposed to.  When a business wants to start up an operation that will produce and potentially add those chemicals into the mix, the cumulative and aggregate exposure may result in an increase in health concerns that would not bee seen if we were only addressing that particular contaminate by itself.  So, to be extra protective, the level (number) applicable to air permitting is derived using an HQ of 0.3.  This is why the TCEQ states:

ESLs are used in the air permitting process to assess the protectiveness of substance-specific emission rate limits for facilities undergoing air permit reviews. Evaluations of modeled worst-case ground-level air concentrations are conducted to determine the potential for adverse effects to occur due to the operation of a proposed facility. They are comparison levels, not ambient air standards. If predicted airborne levels of a chemical exceed its ESL, adverse health or welfare effects would not necessarily be expected to result, but a more in-depth review would be triggered. (7)

AMCVs and ESLs  that are derived from a HQ are for non-cancer causing chemicals.  Air contaminants that are known or suspected carcinogens receive a comparison value derived from a mathematical formula that assumes that at that value there will be no significant risk for cancer.

For a chemical that is listed as a carcinogen, the "no significant risk" level is defined as the level which is calculated to result in not more than one excess case of cancer in 100,000 individuals exposed over a 70-year lifetime. In other words, if you are exposed to the chemical in question at this level every day for 70 years, theoretically it will increase your chances of getting cancer by no more than 1 case in 100,000 individuals so exposed. (5)

For non-cancer causing chemicals and chemicals that show a nonlinear effect, the formula:

• (acute)ESL = 0.3 x (acute)ReV
• (chronic)ESL = 0.3 x (chronic)ReV
• (acute)AMCV = (acute)ReV
• (chronic)AMCV = (chronic)ReV

Both the ESL and the Reference Value (ReV) must be expressed in the same units (micro-grams/cubic meter)  and represent the same exposure period.  This means that if you are going to compare your sample data to an ESL or AMCV, the units and exposure period must be the same.  When Wolf-Environmental and Wilma Subra report 16 volatile organic chemicals exceeded the TCEQ ESLs they used data from a sampling exposure period that was 24 times to long for the short-term and was not averaged over a one year period for the long-term.

This would be like trying to run a restaurant knowing that one coffee pot can effectively serve enough coffee for 100 people per hour. So you hire Wolf Eagle Environmental and Wilma Subra to find out how many coffee pots you need.  They monitor the store for 24 hours and report 800 people.  They then tell you that this exceeded the manufacture's stated value of 100 people by over 8 times!

OK...OK...they were they screwed up when they compared a 24 hour sample to a one hour level.  But were not talking about coffee here.  Even if they had taken the sample for an hour, it appears that they detected Benzene.  And Benzene, according to their reports is a known cancer causing contaminant!  I read on the internets that there is no safe level for a cancer causing compound.  That any exposure increases the risk of cancer.  If there is Benzene in their samples and I am exposed to that, will I get cancer?

Probably not.


Probably?? Is that the best answer you can give?


Well...that's the only answer anyone really can give.  Although - for most chemicals -I can say  with with a very high degree of certainty 'if you stay below this value, you will have no adverse health effects', carcinogens require me to say there is 'no significant risk' if you stay below this level.

Next post:  Air Quality in the Barnett Shale - Part 7: Benzene Exposure and the No Significant Risk Level.

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Air Quality in the Barnett Shale - Part 4: Exceeding TCEQs Short-term ESLs

So what do we know so far:

1. Wolf Eagle Environmental and Wilma Subra used sample results collected from one 24 hour sampling event to compare against Long-term ESLs that are used to evaluate modeled 1-year concentrations.
2. For the seven sample locations, there were a total of 13 times where a chemical detected exceeded the TCEQ's Short-term ESL.
3. TCEQ states that exceeding the ESL "does not necessarily indicate a problem but rather triggers a review in more depth."
4. TCEQ states that “[a]fter several months of operation, state-of-the-art, 24-hour air monitors in the Barnett Shale area are showing no levels of concern for any chemicals. This reinforces our conclusion that there are no immediate health concerns from air quality in the area[.]"

Lets assume that the values obtained from this single 24-hour sampling event represent the amount the citizens of DISH are exposed to, day in, day out.  Because this was a sample collected over a 24 hour period, the 1 hour concentration is equal to 1/24 of the concentration detected and reported.  So, if the highest concentration of benzene reported by Wolf Eagle Environmental was 77.7 ppb (Airfield @1:29) the one hour concentration would be 77.7 / 24 =  3.24 ppb.


Note 2/14/11: I looked at it as an average concentration,  The way TCEQ looked at it, was that there was a single one hour level which was diluted with 23 hours of "clean air."  In re-looking at this, because we are comparing a sample concentration to a one hour ESL (the amount that would be the highest concentration in an hour whereby no adverse health effects would be found) the TCEQ assumption fits better than my averaging assumption.

The reason we divide by 24 is because the sample canister was left on for 24 hours. The Short-term ESLs used by the TCEQ are based on the concentration that would be present in a one hour block of time.  Because we use ppb - or parts of contaminant per billion parts of air - to make comparisons, leaving the canister open for more than one hour would take in more parts of contaminant but the total volume of air would remain the same.  

Canister Sampling is  method of taking a sample of air that uses a stainless steel canister that has been scrupulously cleaned and is under a vacuum. The operator opens the valve on the canister, allowing the air sample to rush into the canister to fill the vacuum. When the canister is opened all at once allowing the air to be sampled over the span of a few seconds, [TCEQ] terms this an instantaneous sample.  A controller can be put on the canister sampler controlling (slowing) the flow of air into the canister over a prescribed time, i.e. 30 minutes, 1 hour, or 24 hours. The samples in the canister are then analyzed on another instrument, typically a gas chromatograph (GC).

TCEQ also recognized this flaw in Wolf Eagle Environmental's reporting but gave them the added benefit of conservatively assuming "that the chemical had a maximum concentration for one hour and was not detected for the remaining 23 hours."  In their memo dated October 29, 2009, TCEQ, in order to compare Wolf Eagle Environmental's 24-hour concentrations with a 1 hour value, multiplied them by 24.  In this manner, the TCEQ compared reported concentrations of the ambient air at the Town of DISH that were 24 times higher than actually detected!  They did, however, note: "This may or may not represent actual conditions."

So now we can add one more to the list of what we know so far

5. Sampling and analysis reported 24 hour concentrations which were compared to ESL values that represent the concentration collected in a one hour period of time.

 Ready for another one?  Yes, there is a number 6.  One more error in their reporting of certain chemicals exceeding TCEQ's ESLs.  The ESLs they used to compare with in their "Revised Air Study Documents" were the wrong type of values to use.


According to the TCEQs AMCV document called "Uses of Effects Screening Levels (ESLs) and Air Monitoring Comparison Values (AMCVs) Revised (May 2010)" Although the same Short-term and Long-term were used for both air permitting and air monitoring, air concentrations of chemicals collected in air monitoring samples represent emissions from multiple chemicals and from different facilities and sources.  For review of air monitoring data, the health-based ReV is appropriate.

ReVs [reference values] are designed to protect the most sensitive individuals in a population by inclusion of uncertainty/variability factors (UFs). UFs account for differences between study animal and human species, variability within the human species, and uncertainties related to the applicability and completeness of the available data. Since UFs are incorporated to address data gaps, variability, and other uncertainties, exceeding the ReV does not automatically indicate that an adverse health effect would occur.

For air permit applications, site-wide modeled concentrations for one chemical at a time are evaluated.  Therefore, for air permitting, an additional buffer is applied to the acute or chronic ReV to calculate the acute and chronic ESLs. The final acute and chronic ESLs developed using the Guidelines are 70% lower than the respective acute and chronic ReV.
  

Because there are "significant differences between performing health effect reviews of air permits and the various forms of ambient air monitoring data," the [TCEQ] has begun using the term “air monitoring comparison values” (AMCVs) in evaluations of air monitoring data.  

AMCVs are chemical-specific air concentrations set to protect human health and welfare. Exposure to an air concentration at or below the AMCVs is not likely to cause adverse health effects in the general public, including sensitive subgroups such as children, the elderly, pregnant women, and people with preexisting health conditions. AMCVs are a collective term that refer to all values used by [TCEQ] staff to review ambient air monitoring data.

The use of different values and different terminology is appropriate because the air monitoring and air permitting programs perform different functions in the protection of human health and welfare."

• The short-term AMCV, based on acute exposure health and welfare data, is compared to monitored concentrations that can be instantaneous or up to 1-hour, which represent a point in time for a specific location.
• The short-term ESL, based on acute exposure health and welfare data, is compared to the modeled 1-hour Maximum Ground Level Concentration (GLCmax).
• The long-term AMCV, based on chronic health and welfare data, is used to evaluate annual averaged monitored concentrations or annual concentrations averaged over multiple years (if available), which represent multiple points in time for a specific locations.
• The long-term ESL, based on chronic or lifetime exposure health and welfare data, is compared to the worst-case annual GLCmax.

So basically, the work performed by Wolf Eagle Environmental looked at the contaminants detected and reported them as if they were being addressed for an air permit.  Lets assume that the values obtained did represent the concentration in air that a citizen of the Town of DISH was going to be exposed to.  What then?

Getting back to benzene and xylene (m & p), how many times was there an exceedence?  And by how much?

Now remember, there are two things in play here.  1st, the ppbv results shown are for 24 hours worth of sampling and could be 24 times higher than what you would have seen if the sample was collected for just one hour.  And 2nd, the ESLs are 70% lower than the reference values.  So, because none of these values exceed the AMCV, we can safely say that exposure to an air concentration at or below the AMCV is not likely to cause an adverse health effect in the general public, including sensitive subgroups such as children, the elderly, pregnant women, and people with preexisting health conditions.

Ignoring the incorrect sampling...ignoring the incorrect comparison, and assuming that these values represent the amount a citizen of the Town of DISH is exposed to, will there be any negative health concerns from these contaminants?

Here is what the TCEQ states in their memo:

The highest potential 1-hour maximum benzene concentration [actual x 24] is below the health effects level observed in short-term animal and human studies; however, it is possible that adverse health effects could occur from exposure to this concentration. It was not possible to determine if residents were exposed to this concentration of benzene based on the information provided.

Here is what I say - and I am not going to far out on a limb: Not likely - because even if you multiplied the contaminate concentrations by 24 like the TCEQ, and even if they exceeded the ESL and the AMCV, there is a margin of safety - uncertainty - built into these comparison values.  It all comes down to how we calculate risk and the value we use in the calculation for the ESL and AMCV.  It's all about the reference value - the ReV.

Air Quality in the Barnett Shale - Part 5:  'n' is for sample size.

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