Evidence for High Rates of Gas Transport in the Deep Subsurface

Stauffer, Philip H.; Rahn, T.; Ortiz, John P.; Salazar, Larry J.; Boukhalfa, Hakim; Behar, Hannah; Snyder, Emily E.

doi:10.1029/2019gl082394

Cited by 17 publications

(13 citation statements)

References 28 publications

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“…Fracture-transport simulations were able to provide an excellent match to the timing of the tracer arrival as well as all 4 of the measured concentrations of tracer in the samples assuming an effective fracture aperture of about 0.5 mm and a permeability of about 800 Darcys for the fracture-filling material. The estimated permeability is lower than that calculated using an idealized model for fracture apertures based on the cubic law 13 . Such a narrow, material-filled fracture would be extremely difficult or impossible to detect by any means other than localizing the soil-gas flux using a tarp-and-sample system such as that deployed in this study.…”

Section: Discussioncontrasting

confidence: 63%

Gas transport across the low-permeability containment zone of an underground nuclear explosion

Carrigan

Sun

Hunter

et al. 2020

Sci Rep

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Understanding the nature of gas transport from an underground nuclear explosion (Une) is required for evaluating the ability to detect and interpret either on-site or atmospheric signatures of noble gas radionuclides resulting from the event. We performed a pressure and chemical tracer monitoring experiment at the site of an underground nuclear test that occurred in a tunnel in nevada to evaluate the possible modes of gas transport to the surface. the site represents a very well-contained, low gaspermeability end member for past Unes at the nevada national Security Site. However, there is very strong evidence that gases detected at the surface during a period of low atmospheric pressure resulted from fractures of extremely small aperture that are essentially invisible. our analyses also suggest that gases would have easily migrated to the top of the high-permeability collapse zone following the detonation minimizing the final distance required for migration along these narrow fractures to the surface. this indicates that on-site detection of gases emanating from such low-permeability sites is feasible while standoff detection of atmospheric plumes may also be possible at local distances for sufficiently high fracture densities. Finally, our results show that gas leakage into the atmosphere also occurred directly from the tunnel portal and should be monitored in future tunnel gas sampling experiments for the purpose of better understanding relative contributions to detection of radioxenon releases via both fracture network and tunnel transport.

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Section: Discussioncontrasting

confidence: 63%

Gas transport across the low-permeability containment zone of an underground nuclear explosion

Carrigan

Sun

Hunter

et al. 2020

Sci Rep

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“…The landfill source includes the trenches in the waste facility. Biological sources may emit VOCs in the subsurface directly, or aboveground emissions may enter the subsurface by diffusion and by barometric pumping (Auer et al, 1996; Choi et al, 2002; Stauffer et al, 2019). Elevated CO 2 near the water table at the ADRS indicated potential georespiration (Walvoord et al, 2005; Conaway et al, 2018), in which microbes respire relict carbon.…”

Section: Methods: Field Site Sampling Analysis and Statistical Appmentioning

confidence: 99%

Spatial Fingerprinting of Biogenic and Anthropogenic Volatile Organic Compounds in an Arid Unsaturated Zone

Green

Luo

Conaway

et al. 2019

Vadose Zone Journal

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17 years of VOC data show variations around and far from a mixed‐waste landfill. Principal components analysis fingerprints landfill and ambient VOCs. Biogenic VOCs occur throughout the deep unsaturated zone and outnumber landfill VOCs. Anthropogenic and biogenic sources at a single site complicate analysis of VOC transport. Subsurface volatile organic compounds (VOCs) can pose risks to human and environmental health and mediate biological processes. Volatile organic compounds have both anthropogenic and biogenic origins, but the relative importance of these sources has not been explored in subsurface environments. This study synthesized 17 yr of VOC data from the Amargosa Desert Research Site in Nevada with the goal of improving understanding of spatial and temporal variations that distinguish sources of VOCs from a landfill and from ambient sources including biogenic VOCs (bVOCs). Gas samples were collected from 1999 to 2016 from an array of shallow sample points (0.5‐ and 1.5‐m depth) and from vertical profiles at three deep boreholes: two (109 m deep) near the border of a waste facility (33 and 100 m distant), and one (29 m deep) in a remote area 3 km to the south. Samples were analyzed for target VOCs and a subset was analyzed for non‐target VOCs to enumerate a greater variety of potential bVOCs. Principal components analysis of the target and non‐target VOCs provided an assessment of the spatial variability of VOCs originating from the landfill site and from ambient sources. Ambient VOCs occurred at all sample sites across a range of depths, and most were consistent with biogenic origins, indicating for the first time the presence of bVOCs in the deep unsaturated zone. Because some VOCs have both anthropogenic and biogenic sources, discrimination of sources can be important for estimating the extent and migration of anthropogenic plumes in arid unsaturated zones.

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“…In general, spatial gradients in the atmospheric pressure rarely exceed 3.0 hPa per 100 km (Miller & Thompson, 1970). Hence, the atmospheric pressure on the local or experimental site scale can be assumed unsteady but uniform (Massmann & Farrier, 1992), and the entire vadose zone can be compressed as the atmospheric pressure increases (Stauffer et al, 2019).…”

Section: Diurnal Characteristics Of the Earth-air Pressurementioning

confidence: 99%

Effect of earth–air breathing on evaporation of deeply buried phreatic water in extremely arid regions

Zhan

Wang

et al. 2021

Hydrological Processes

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In extremely arid regions, deeply buried phreatic water evaporates during the daytime from March to November in the northern hemisphere. It has been found that the earth-air undergoes 'autonomous breathing' and 'passive breathing', respectively caused by the changes of temperature and atmospheric pressure. In this paper, the effects of these breathing modes on phreatic evaporation (PhE) were investigated as well as the responsible mechanisms. Quantitative estimates suggest that the direct contribution from autonomous breathing is only 0.55 gÁm −2 Áyr −1 . Passive breathing pumps water vapour upwards from the deeply buried phreatic water table. Film water on the soil continuously migrates in pulsation from deep layers to the upper layer. Na 2 SO 4 in the shallow soil absorbs moisture from the earth-air at night and decomposes during the day, forming water vapour, which is critical to the occurrence of PhE. The diurnal PhE process can be elucidated in detail by the bimodal variation in the atmospheric pressure. PhE occurs mainly from 10:00 to 17:00 during daytime from March to November, which correlates with passive breathing of the earth-air.The amplitude of atmospheric fluctuation determines the amount of earth-air that outflows, while temperature determines the water vapour concentration. In calculation, PhE is equal to the net absolute humidity (AH) times the amount of earth-air.There is 1.55 mmÁyear −1 of PhE caused by daily peak!valley differences, and about 2.97 mmÁyear −1 in estimation caused by numerous atmospheric fluctuations smaller than 2.84 hPa. The results coincide with the actual amount of PhE monitored of 4.52 mmÁyear −1 . Therefore, the amount of PhE is proportional to the range and frequency of fluctuation in external atmospheric pressure, and is also positively related to soil temperature, salt content, water content, porosity, and vadose zone thickness.

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Evidence for High Rates of Gas Transport in the Deep Subsurface

Cited by 17 publications

References 28 publications

Gas transport across the low-permeability containment zone of an underground nuclear explosion

Gas transport across the low-permeability containment zone of an underground nuclear explosion

Spatial Fingerprinting of Biogenic and Anthropogenic Volatile Organic Compounds in an Arid Unsaturated Zone

Effect of earth–air breathing on evaporation of deeply buried phreatic water in extremely arid regions

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