Field measurements of tracer gas transport by barometric pumping
- Lagus Applied Technology, San Diego, CA (United States)
- Lawrence Livermore National Lab., Mercury, NV (United States)
- Lawrence Livermore National Lab., CA (United States)
Vertical gas motions induced by barometric pressure variations can carry radioactive gases out of the rubblized region produced by an underground nuclear explosion, through overburden rock, into the atmosphere. To better quantify transit time and amount of transport, field experiments were conducted at two sites on Pahute Mesa, Kapelli and Tierra, where radioactive gases had been earlier detected in surface cracks. At each site, two tracer gases were injected into the rubblized chimney 300-400 m beneath the surface and their arrival was monitored by concentration measurements in gas samples extracted from shallow collection holes. The first ``active`` tracer was driven by a large quantity of injected air; the second ``passive`` tracer was introduced with minimal gas drive to observe the natural transport by barometric pumping. Kapelli was injected in the fall of 1990, followed by Tierra in the fall of 1991. Data was collected at both sites through the summer of 1993. At both sites, no surface arrival of tracer was observed during the active phase of the experiment despite the injection of several million cubic feet of air, suggesting that cavity pressurization is likely to induce horizontal transport along high permeability layers rather than vertical transport to the surface. In contrast, the vertical pressure gradients associated with barometric pumping brought both tracers to the surface in comparable concentrations within three months at Kapelli, whereas 15 months elapsed before surface arrival at Tierra. At Kapelli, a quasisteady pumping regime was established, with tracer concentrations in effluent gases 1000 times smaller than concentrations thought to exist in the chimney. Tracer concentrations observed at Tierra were typically an order of magnitude smaller. Comparisons with theoretical calculations suggest that the gases are traveling through {approximately}1 millimeter vertical fractures spaced 2 to 4 meters apart. 6 refs., 18 figs., 3 tabs.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); S-Cubed, La Jolla, CA (United States); Lagus Applied Technology, San Diego, CA (United States); Lawrence Livermore National Lab., Mercury, NV (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 225021
- Report Number(s):
- UCRL-CR-119147; ON: DE96009899; IN: SSS-DFR-94-14725; TRN: 96:012749
- Resource Relation:
- Other Information: PBD: 28 Jul 1994
- Country of Publication:
- United States
- Language:
- English
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