So today I am writing my blog while dressed in a long sleeve shirt - with tie - slacks, and my recently polished dress shoes (black to match my belt according to my wife). And to complete this outfit of visual competency and authority, I have put on my white lab coat, the one with my name embroidered over the pocket!
Hopefully this will get my street cred' back. You know, nothing says "scientist" like a white lab coat! In fact, look at what these two guys at Columbia Analytical Services are wearing:
You know what else you can find on their website? This:
Do you know what "COS" and "CS2" is? Well since I am wearing a white lab coat, I do.
- COS = Carbonyl sulfide
- CS2 - Carbon disulfide
Do those two chemicals sound familiar to you? Well they do to me:
This post today is only going to focus on Plot 2 of the FWLN report. Plot 2 is based on the concentration of carbonyl sulfide found in sample QLA5DC-1.
According to the white lab coats at Columbia Analytical Services, there are two factors in play when a Tedlar bag is used to collect a gas sample.
- Concentration range is from ppm to percent (1 percent = 10,000 ppm)
- Artifacts may be produced which include carbonyl sulfide and carbon disulfide
...and artifacts were acknowledged:
...and the concentrations were reported as ppbv (which are 1000 times smaller than a ppm):
Now all of this give me pause - and when I am wearing my white lab coat - my scientist-senses start to tingle (analogous to Spider-Man's spider-sense telling him that something is wrong) - or it could just be my cell phone set on vibrate. Anyway....
So what's the issue? Seems that Plot 2 which was used in the FWLN shows "multiples [that] were 6 times the health benchmark for carbonyl sulfide."
And how did they arrive at this "6 times" number? Using a "backed in" emission rate calculated by Dr. Sattler as described in her 3/7/11 draft report titled "Dispersion Modeling of Carbonyl Sulfide Emissions from a Natural Gas Compressor Station near Lake Arlington." (link not available).
In this report Dr. Sattler describes the sample concentrations for carbonyl sulfide she used as follows:
...which corresponds to these samples in the BEECE report:
...which are associated with these two laboratory reports:
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| Upwind Sample |
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| Downwind Sample |
Now there are two factors seen above that get my spider-senses....err my white lab coat senses buzzing. The first is that there is no data qualifier "+" for the carbonyl sulfide quantification as there is for carbon disulfide.
Note 3/14/11: Spoke with the lab this morning. the reason that there is no qualifier is that they set the highest number attributable to an artifact at 25 ppb. This qualifier number is dependent on the Tedlar bag used. So the quantity of 130 ppbv may be only as high as 105 ppbv if the bag did produce artifacts of carbonyl sulfide. By the way, I just noticed that the laboratory that performed the analysis was the same lab with the white lab coat guys that produced the table I used above. It's a small world.
Note 3/14/11: Spoke with the lab this morning. the reason that there is no qualifier is that they set the highest number attributable to an artifact at 25 ppb. This qualifier number is dependent on the Tedlar bag used. So the quantity of 130 ppbv may be only as high as 105 ppbv if the bag did produce artifacts of carbonyl sulfide. By the way, I just noticed that the laboratory that performed the analysis was the same lab with the white lab coat guys that produced the table I used above. It's a small world.
Was this an oversight or were they able to exclude the possibility of an artifact in this sample? The reason that I question this is that the possibility of the carbonyl sulfide being an artifact is noted in samples:
QA52DW-1, EMR3DE-1, EMR3DW-1, CAP4UC-1, CAP4DC2-1, CAP4DC2-DUP1, DLB6U-1, DLB6DE-1, DHH7U-1, CLP9UC-1, XRA4UE-1, and XRA4DE-1
In other words, out of 18 samples 12 identify the carbonyl sulfide as a "possible Tedlar bag artifact." I will be contacting the laboratory next week to see if I can find out if this was in error.
The second reason I question the validity of these carbonyl sulfide results is that even though the laboratory may feel quite confident in the numbers they have reported for ASTM Method D5504-08 for sulfur compounds:
...while wearing my white lab coat, I went and read the ASTM method.
...and here is what I found out:
...so we have to assume that both the sampler and the laboratory understood this and took the proper precautions. Okay, so lets assume they did. What next?
...well the test is for the gas itself...may not be appropriate for ambient air samples...still...rang is 0.01 ppm...what's that in ppb?....if 1000 ppb = 1 ppm, the range is down to 10 ppb...okay that means the 130 ppb is 130/1000 = 0.13 ppm....kind of close to the method's limit....okay....odd though, the lab's MRL states they can "confidently" go down to 0.0078 ppm.
So once again we are looking at the identification and quantification of a contaminant of concern that is questionable. I am unsure why ASTM D5504-08 was utilized in the first place. Most likely it was to look for sulfur contaminants that are common to natural gas and are not picked up by EPA Method TO-15. In any case, the use of a Tedlar bag was possibly the wrong choice if carbon disulfide and carbonyl sulfide were to be reported.
Hey....but wait a second....isn't TO-15 appropriate for carbon disulfide and carbonyl sulfide?
And didn't BSEEC run a TO-15 analysis on sample QLA5DC-1 from which Dr. Sattler obtained the quantity for her backed in emission rate calculation for her carbonyl sulfide model shown in plot 2?
...which means there should be a lab report for this sample showing the quantity of carbon disulfide and carbonyl sulfide in the same air on the same day. And this sample is the correct method and does not have any footnotes calling into question its validity, such as a "possible artifact." So looking at the lab results for sample QLA5DC-1 we see:
Doh! They didn't analyze for carbonyl sulfide! Had they tested for carbonyl sulfide with TO-15 it would have been much more definitive and I could have ended this post right here and now stating that the carbonyl sulfide reported was indeed an artifact. If only it would be that easy....
Still, there is good evidence to think it is - most likely - an artifact.
The TO-15 method has a detection limit for carbon disulfide of 0.236 ppbv. The TO-15 results for 46 one hour samples show non-detect and two samples show carbon disulfide at less than 0.61 ppbv. Now compare this to the detection of carbon disulfide with ASTM Method D5504-08 which found carbon disulfide in 12 out of 21samples with a high concentration of 11 ppbv.
And with my white lab coat on - complete with embroidered name over the pocket - I am able to look at this and boldly state that Plot 2 in the FWLN report is based on a positive identification of carbonyl sulfide and a quantitative amount that is suspect.
And if Peter Parker (aka: Spider-Man) - who himself is a scientist - was looking at this, he too would see not a criminal number, but a number that is suspect. Call it his spidey-sense, objectivity, or just plain-ol' scientific common knowledge, but that's what any good scientist would conclude - even one that uses self-depreciation and comic book characters to try and drive home his point.
The thing is, we scientists are only as good as the numbers we use and the place we get our data from. And because of this, the air dispersion model that generated Plot 2 that was based on the results from sample QLA5DC-1, which was derived using ASTM Method D5504-08 from samples collected in a Tedlar bag which - according to other scientists wearing white lab coats - are designed for samples in the ppm range and are also known to produce artifacts of COS and CS2, which - while wearing my white lab coat - I have identified as the two culprits of concern in the FWLN report regarding the need for set-backs; carbonyl sulfide and carbon disulfide, makes the model's predictions of "multiples [that] were 6 times the health benchmark for carbonyl sulfide" suspect.
So what are we left with now?
If the FWLN report is based on Plot 1 for carbon disulfide which was derived from one single sample collected on one single day (see post) and Plot 2 is based on carbonyl sulfide derived from using ASTM Method D5504-08, then nothing definitive, conclusive, alarming, substantiating, or realistic regarding set-back distance can be ascertained.
Next Post: Air Quality in the Barnett Shale - Part 28: Why Plot 2 used Carbonyl Disulfide
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