Ambient air monitoring

[Nkhurd]

Hello everyone:
I'm involved in designing a sampling plan to collect ambient air samples (VOCs and H2S) along the fenceline of a waste disposal facility. This facility has a dike (approx. 8 ft high and 6-7 ft wide) as its fenceline. The topography around the facility primarily consist of flat terrain with shrubs and marsh land. We plan to place the samplers as suggested in EPA guidance documents. However, there is a good chance that such technically appropriate sampling locations might be inaccessible. In that case the only sampling location(s) practically possible would be sampling on the dike and am not sure if it is appropriate to collect samples on these dikes which are almost 8 ft high. Please comment providing a rationale for your suggestion.
Thank you,
Nandan

 

[jheidt2543]

I am not sure why you say ..."the only sampling location(s) practically possible would be sampling on the dike and am not sure if it is appropriate to collect samples on these dikes which are almost 8 ft high." I am not familiar with the EPA guidlines for takeing air samples.

There is an ongoing air sampling project in my city where the samples are taken at the level of the rooftop. An 8' sample height is basically ceiling height, so as long as the sample locations and elevations are documented I should think you would still be collecting valid information.

I think you could devise a plan that would include the ability to correlate samples at the 8' level with samples at the level you want.

 

[Fizzhead]

If you are collecting samples to document the VOC's and H2S coming from the site, then you may be able to correlate sample results from the dike locations with results from other locations (i.e., your control, or upwind, locations) to determine if you are getting representative results. The real problem is that when the samplers are located too close to the site, you may miss measurement of actual emissions that are laterally displaced from the sampler. Locating the samplers at the EPA recommended distances from the site is intended to minimize the chances of that happening because the gasses have laterally dispersed to a greater degree. If your site is not too large, or the VOC and H2S sources within the site are well documented you might be able to reduce this error, but local variations in wind direction will always produce a relatively large error component in your measurements that you may not be able to accommodate. One possible, but expensive, way to offset this error is to increase the number of sample stations along a line normal to the predominant local wind direction. Finally, the elevated position atop the dikes are of course somewhat locally distinct, based upon your description of the local topography. You will need to vary the elevation to determine potential effects and then optimize your sampler inlet elevation. Again, this is going to be affected by the local wind variations day to day, so it's not an easy process. Good Luck!

 

[DRsquare]

It also depends what question you are trying to answer. I assume you want something like concentration or mass emissions. Concentration of course depends on dilution (wind speed). Mass emissions require determination of emission profile with height and direction. Emission rate is also dependant on wind speed, it affects transfer rate from the surface. Most treatment systems are at an elevated temperature and moisture, so you have bouyency consideration.

Also measuring H2S is not a trivial project. It is not stable in cannisters at ppb levels, even in glass lined SS cans. It will oxidize if stored in air, it can be lost in the moisture in the can, it can be lost in the measuring device very easily, etc. I've spent the better part of 20 years (pulp and paper industry) measuring sulfur gases at industrial, workplace and ambient levels. My last project before being downsized was trying to determine emission rates from wastewater treatment facilities to develop emission rate correlations with aqueous levels.

Better make sure that you know what levels you need to measure and do some lab work, including the sampling method, to make sure you can. A lot of work has also been done in the agricultural (swine) industry, and can be found online.