The bubble stripping method for determining dissolved hydrogen (H-2) in well water

The bubble stripping method was developed for use at field sites to measure the concentration of dissolved hydrogen (H-2) in ground water. This inform ation is useful in assessing the viability of employing monitored natural a ttenuation (MNA) as a strategy to influence the restoration of sites contam inated with chlorinated solvents. In laboratory studies, a reservoir contai ning water was employed to simulate a well. The system was constructed so t hat the concentration of dissolved H-2 could be maintained at a constant le vel. The method was applied by pumping water from the reservoir into a samp le cell, and then injecting 20 ml of nitrogen into the cell to produce a he adspace (the "bubble"). Stripping was accomplished by pumping water through the cell, which produced agitation between the aqueous phase and the heads pace. Pumping was continued for a length of time sufficient for dissolved H -2 to partition between the two phases. Analysis of H-2 in the headspace by gas chromatography enabled the concentration of dissolved H-2 in solution to be calculated with the use of Henry's law. Two sample cell designs were compared in this study, the Microseeps Cell and the Chapelle Cell. Kinetics of equilibration studies were conducted with each cell, employing solution flow rates of 200, 300, and 400 ml/min, at 4 and 21 degreesC. The Microsee ps Cell compared favorably with the Chapelle Cell with regards to kinetics of equilibration, with the added benefit of costing significantly less. (C) 2000 John Wiley & Sons, Inc.