Effect of subsurface soil moisture variability and atmospheric conditions on methane gas migration in shallow subsurface

Deepagoda, T.K.K. Chamindu; Smits, Kathleen M.; Oldenburg, Curtis M.

doi:10.1016/j.ijggc.2016.10.016

Cited by 50 publications

(35 citation statements)

References 48 publications

(45 reference statements)

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“…Experiments in both systems were conducted for near‐dry (ND) (i.e., at residual water saturation) and partially saturated (PS) (i.e., wet‐packed and drained to ‐35 cm H 2 O with respect to the center of the tank) conditions. The soil physical properties relevant to the present study are given in Deepagoda et al . A diffusive point gas source (50,000 ppm CH 4 and 950,000 ppm N 2 , flow rate = 0.5 Lmin −1 was placed 2 cm above the bottom of the sand‐packed tank (at the centerline, × = 27.5 cm measured from the downstream edge) to mimic a leak from a shallow underground pipe.…”

Section: Methodsmentioning

confidence: 99%

Effect of varying atmospheric conditions on methane boundary‐layer development in a free flow domain interfaced with a porous media domain

2017

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Mitigation of atmospheric emission of methane from leaky underground infrastructure is important for controlling the global anthropogenic greenhouse gas burden. Overexposure to methane may also cause occupational health problems in indoor/outdoor environments at the local scale. Subsurface soil conditions (e.g. soil heterogeneity) affect methane migration in soils while near‐surface atmospheric boundary conditions (e.g. wind and temperature) affect off‐site emissions across the soil‐atmosphere interface. This study investigated the above‐surface methane concentration boundary‐layer development under different soil conditions (homogenous and layered) and atmospheric boundary controls (wind and temperature). A series of controlled bench‐scale experiments was conducted using an open‐loop boundary‐layer wind tunnel interfaced with a porous media tank inside which a simulated methane point source was embedded to mimic a buried leaky pipeline. Results revealed pronounced effects of wind and, to a lesser extent, temperature on above‐surface methane boundary‐layer development. High atmospheric temperature contributed to the concentration boundary‐layer build‐up whereas high wind velocity caused erosion of the boundary layer. The boundary‐layer methane concentration profiles were adequately simulated within an advection‐diffusion modeling framework combined with a Navier‐Stokes free flow domain by coupling free air flow, heat flow and flow of a multicomponent gas mixture. Simulations further implied that the Fickian diffusion approach may have limited applications when pronounced non‐isothermal conditions prevail within the system. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

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Section: Methodsmentioning

confidence: 99%

Effect of varying atmospheric conditions on methane boundary‐layer development in a free flow domain interfaced with a porous media domain

2017

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“…The effect is expected to increase with an increase in wind velocity. Second, gas component concentrations above the soil surface increase in wind-downstream direction due to the accumulation of gas components inside the laminar boundary layer (as has been shown by Chamindu Deepagoda, Smits, & Oldenburg, 2016;Chamindu Deepagoda et al, 2018). Consequently, concentration gradients across the surface are higher at the wind-upstream side of the sand tank than at the downstream side, thereby causing lower concentrations at transect OA than at transect OC.…”

Section: Water Resources Researchmentioning

confidence: 92%

“…The setup is adaptable for different gases. It was inspired by previous gas transport and evaporation experiments in coupled systems of porous medium and free flow, where a sand tank is placed underneath a wind tunnel (Chamindu Deepagoda et al, 2018;Chamindu Deepagoda, Smits, & Oldenburg, 2016;Davarzani et al, 2014). Such systems allow for high control over test conditions and possess clearly defined domain boundaries for both the porous medium and the overlying wind field, which is ideal for subsequent numerical studies.…”

Section: Experimental Designmentioning

confidence: 99%

“…Gas supply is controlled by a regulation valve and a mass flow meter (Omega, model FMA-1607A, range 0.05 to 10 slpm, accuracy 0.8%). An inflow rate of 0.5 slpm (¼ 0.2 mol/s) was applied, representing a diffusion-dominant leak from a shallow subsurface source, as described in Chamindu Deepagoda, Smits, and Oldenburg (2016) and also in Ulrich et al (2019). Chamindu Deepagoda, Smits, and Oldenburg (2016) found measurable influences of wind velocity on the concentration profile inside the soil and on concentrations above the soil surface.…”

Section: Water Resources Researchmentioning

confidence: 99%

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Gas Component Transport Across the Soil‐Atmosphere Interface for Gases of Different Density: Experiments and Modeling

Bahlmann

Smits

Heck

et al. 2020

Water Resources Research

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We investigate the influence of near-surface wind conditions on subsurface gas transport and on soil-atmosphere gas exchange for gases of different density. Results of a sand tank experiment are supported by a numerical investigation with a fully coupled porous medium-free flow model, which accounts for wind turbulence. The experiment consists of a two-dimensional bench-scale soil tank containing homogeneous sand and an overlying wind tunnel. A point source was installed at the bottom of the tank. Gas concentrations were measured at multiple horizontal and vertical locations. Tested conditions include four wind velocities (0.2/1.0/2.0/2.7 m/s), three different gases (helium: light, nitrogen: neutral, and carbon dioxide: heavy), and two transport cases (1: steady-state gas supply from the point source; 2: transport under decreasing concentration gradient, subsequent to termination of gas supply). The model was used to assess flow patterns and gas fluxes across the soil surface. Results demonstrate that flow and transport in the vicinity of the surface are strongly coupled to the overlying wind field. An increase in wind velocity accelerates soil-atmosphere gas exchange. This is due to the effect of the wind profile on soil surface concentrations and due to wind-induced advection, which causes subsurface horizontal transport. The presence of gases with pronounced density difference to air adds additional complexity to the transport through the wind-affected soil layers. Wind impact differs between tested gases. Observed transport is multidimensional and shows that heavy as well as light gases cannot be treated as inert tracers, which applies to many gases in environmental studies.

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“…Henry's law models dissolution of gaseous methane in the aqueous phase, with Henry's coefficients, estimated using the method explained by Cramer (1982). Previous studies have evidenced a good agreement with measured methane concentrations and simulations from TOUGH2-EOS7CA under different subsurface soil conditions (e.g., Chamindu Deepagoda, Smits, & Oldenburg, 2016), hence proved to be promising numerical tool to estimate subsurface methane migration in the absence of direct concentration measurements.…”

Section: Numerical Simulationmentioning

confidence: 95%

Effects of “soil‐like” particle size on gas transport and water retention properties in aged municipal solid waste from a Sri Lankan open dumpsite

Shanujah

Deepagoda

Karunarathna

et al. 2020

Soil Science Soc of Amer J

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Open dumps constitute a major source of greenhouse gases (GHGs), predominantly methane and carbon dioxide, in developing countries. In an aged dump, typical waste composition is dominated by the “soil‐like” fraction of which physical, hydraulic and gas transport characteristics markedly affect GHG emissions. This study characterized soil‐gas diffusivity (Dp/D0), soil‐water characteristics (SWC), and particle size distribution in “soil‐like” fractions of aged solid waste retrieved at 2.5–5 m depth from an old open dumpsite situated at Kurunegala, Sri Lanka. The “soil‐like” fraction was proportioned into three groups based on particle size (0–4.75, 4.75–9.5, and 9.5–25 mm) to investigate the particle size effect on Dp/D0 and SWC. The simulated methane concentration profiles in different size groups were also examined using the transport simulator TOUGH2‐EOS7CA based on the multiphase flow of multicomponent gas mixture (methane, water vapour and air) under dry and half‐saturation conditions across a predefined temperature gradient. The results highlighted distinct two‐region characteristics (i.e., inter‐aggregate and intra‐aggregate pore regions) in all three size fractions which could be adequately parameterized with existing and modified bimodal functions. We proposed a useful practical tool for estimating Dp/D0 for known mean particle size and volumetric water content in the absence of direct measurements. The results further revealed that Dp/D0 is particle‐size dependent; however, Dp/D0 remained invariant across all size fractions at the volumetric water content of ∼0.22–0.25 cm3 cm−3. Numerical results further showed a pronounced effect of particle size and soil moisture on gas transport properties.

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Effect of subsurface soil moisture variability and atmospheric conditions on methane gas migration in shallow subsurface

Abstract:  Soil heterogeneity has a distinct effect on surface methane concentrations.  Methane transport can be adequately represented with a Fickian model framework.  Saturation has a dominant effect over soil texture on gas migration through soil.

Cited by 50 publications

References 48 publications

Effect of varying atmospheric conditions on methane boundary‐layer development in a free flow domain interfaced with a porous media domain

Effect of varying atmospheric conditions on methane boundary‐layer development in a free flow domain interfaced with a porous media domain

Gas Component Transport Across the Soil‐Atmosphere Interface for Gases of Different Density: Experiments and Modeling

Effects of “soil‐like” particle size on gas transport and water retention properties in aged municipal solid waste from a Sri Lankan open dumpsite

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