Fh. Chapelle et al., PRACTICAL CONSIDERATIONS FOR MEASURING HYDROGEN CONCENTRATIONS IN GROUNDWATER, Environmental science & technology, 31(10), 1997, pp. 2873-2877
Several practical considerations for measuring concentrations of disso
lved molecular hydrogen (H-2) in groundwater, including (1) sampling m
ethods, (2) pumping methods, and (3) effects of well casing materials
were evaluated. Three different sampling methodologies (a downhole sam
pler, a gas-stripping method, and a diffusion sampler) were compared.
The downhole sampler and gas-stripping methods gave similar results wh
en applied to the same wells. The diffusion sampler, on the other hand
, appeared to overestimate H-2 concentrations relative to the downhole
sampler. Of these methods, the gas-stripping method is better suited
to field conditions because it is faster (similar to 30 min for a sing
le analysis as opposed to 2 h for the downhole sampler or 8 h for the
diffusion sampler), the analysis is easier (less sample manipulation i
s required), and the data computations are more straightforward (H-2 c
oncentrations need not be corrected for water sample volume). Measurem
ent of H-2 using the gas-stripping method can be affected by different
pumping equipment. Peristaltic, piston, and bladder pumps all gave si
milar results when applied to water produced from the same well. It wa
s observed, however, that peristaltic-pumped water (which draws water
under a negative pressure) enhanced the gas-stripping process and equi
librated slightly faster than either piston or bladder pumps (which pu
sh water under a positive pressure). A direct current(dc) electrically
driven submersible pump was observed to produce H-2 and was not suita
ble for measuring H-2 in groundwater. Measurements from two field site
s indicate that iron or steel well casings produce H-2, which masks H-
2 concentrations in groundwater. PVC-cased wells or wells cased with o
ther materials that do not produce H-2 are necessary for measuring H-2
concentrations in groundwater.