Dissolved hydrogen is the dreaded analysis in every field tech?s Sampling & Analysis Plan.? Yes, there?s more equipment to lug around, the risk of impaling yourself with a 1-inch long needle, and those pressed wood ring stands that swell and warp at just the threat of a summer thunderstorm. ?But it?s important!? It is!? And if I were an expert on assessing the progress and/or potential of bioremediation as well as the development of necessary support for regulatory acceptance of remediation work in order to characterize dominant reduction processes for contaminant degradation through the use of a simple little parameter like hydrogen1, I?d tell you why!? But I?m not, so I won?t.
Instead, I?ll tell you four important facts that everyone should know about hydrogen sampling:
1. Hydrogen sampling takes a long time
I repeat (through a bull horn), IT TAKES A LONG TIME!? The additional time should be considered even before field work planning – – I?m talking proposal stage.? According to Microseeps, it takes 15-20 minutes to equilibriate the introduced air bubble with the groundwater using a bubble of 20 ccs and a groundwater flow rate of 250 to 300 ccs per minute.? In addition to this time, there is additional set up and break down of the hydrogen gas stripping cell. As a result, proposal pricing needs to reflect an additional 25 to 30 minutes of labor per person per well. If you do not consider this extra time, there?s really no other way for me to state this:? You?re screwed.
2. Do not perform hydrogen sampling on newly installed wells; it?s a complete waste of time
Dissolved hydrogen results will not be representative until approximately 3 months following monitoring well installation; however, other parameters may be sampled for following monitoring well development.
3. Well construction materials matter
A study entitled Practical Considerations for Measuring Hydrogen Concentrations in Groundwater found that iron and steel well casings produce hydrogen, which masks hydrogen concentrations in groundwater, and that PVC-cased wells are necessary for obtaining representative hydrogen concentrations.
4. Be particular about your pump
Electrically-driven submersible pumps can introduce hydrogen due to electrochemical interactions with the sampled water.? In fact, in this study, concentrations of dissolved hydrogen were approximately two orders of magnitude higher when sampling was performed with an electrically driven submersible pump versus a bladder or peristaltic pump.
5. Dissolved hydrogen is not an analysis commonly performed within environmental laboratories
Often, even nation-wide companies will subcontract to labs like Microseeps or VaporTech Services.? If you encounter issues with any of the hydrogen equipment, you aren?t clear on the methodology, or you have been swearing for at least 10 minutes and have the urge to run over the hydrogen gas stripping cell with your truck, I would encourage you to contact the subcontracted lab directly for assistance.
Written by: Karen Baer