title: Quantifying (12/13)CH(4) migration and fate following sub-surface release to an agricultural soil.
abstract: Following gas generation in a Geological Disposal Facility (GDF), (14)C-containing gases could migrate through the geosphere, eventually diffusing into soils at the Earth's surface. This paper reports summary results from laboratory and field experiments to obtain information on the probable rates of a) diffusive transport and b) oxidation of (12/13)CH(4) (as a surrogate for (14)CH4) in a typical agricultural soil in the UK. Rates of CH(4) oxidation were generally low in the field and undisturbed soil columns, though a re-packed column of homogenised topsoil oxidised ambient atmospheric CH(4) 20× faster than an undisturbed soil column. In contrast to low observed rates of CH(4) oxidation, the effective diffusion of CH(4) through the soil was rapid. Isotopically labelled CH(4) injected at a depth of 45 cm in the field diffused to the surface and exited the soil over a time period ranging from 8 to 24 h. The rate of CH(4) diffusion through the soil was increased by the presence of ryegrass roots which increased soil porosity and decreased water content. δ(13)C values for laboratory column soils after labelled CH(4) injection experiments showed no sign of residual (13)C, despite the extremely high δ(13)C values of the injected (12/13)CH(4). If laboratory observations are confirmed by measurements in field samples it can be concluded that the majority of (14)CH(4) from a GDF which enters a soil with low methanotrophic activity will be lost to the free atmosphere after diffusing rapidly through the soil column.
authors: University of Nottingham, School of Biosciences, Sutton Bonington, Leicestershire LE12 5RD, UK. Electronic address: george.shaw@nottingham.ac.uk.
authors: G
authors: G
authors: Shaw
authors: University of Nottingham, School of Biosciences, Sutton Bonington, Leicestershire LE12 5RD, UK.
authors: B
authors: B
authors: Atkinson
authors: University of Nottingham, Faculty of Engineering, Nottingham NG7 2RD, UK.
authors: W
authors: W
authors: Meredith
authors: University of Nottingham, Faculty of Engineering, Nottingham NG7 2RD, UK.
authors: C
authors: C
authors: Snape
authors: School of Geography, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor, Malaysia.
authors: M
authors: M
authors: Steven
authors: AMEC, Harwell, Oxon OX11 0QB, UK.
authors: A
authors: A
authors: Hoch
authors: AMEC, Harwell, Oxon OX11 0QB, UK.
authors: D
authors: D
authors: Lever
mesh_terms: D000383:Agriculture; D002250:Carbon Radioisotopes / Q000032:analysis; D008697:Methane / Q000032:analysis*; D012037:Refuse Disposal; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology
chemical_list: D002250:Carbon Radioisotopes; D012987:Soil; D008697:Methane
keywords: Carbon-14; Gas migration; Geological disposal facility; Methane; Radioactive waste