| Abstract
| - A simple in-situ passive dissolved gas groundwatersampler, comprised of a short length of silicone tubingattached to a gastight or other syringe, was adapted andtested for in-situ collection of equilibrium gas samples.Sampler retrieval after several days of immersion ingroundwater allowed the direct injection of the sampleonto a gas chromatograph (GC), simplifying field collectionand sample handling over the commonly used “bubblestripping” method for H2 analyses. A GC was modified bysequencing a thermal conductivity (TC) detector followedby a reductive gas (RG) detector so that linear calibrationof H2 over the range 0.2−200 000 ppmv was attainedusing a 0.5-mL gas sample; inclusion of the TC detectorallowed the simultaneous quantification of other fixed gases(O2, CO2, He, and Ne) to which the RG detector was notresponsive. Uptake kinetics for H2 and He indicated that thepassive sampler reached equilibrium within 12 h ofimmersion in water. Field testing of these passive samplersrevealed unusually large equilibrium gas-phase H2concentrations in groundwater, ranging from 0.1 to 13.9%,by volume, in 11 monitoring wells surrounding fourformer radiological wastewater disposal ponds at theY-12 plant in Oak Ridge, Tennessee.
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