The distribution of CH4 in unsaturated glacial and eolian deposits adjacent to buried low-level radioactive waste was measured, and movement of the gas from the waste source was simulated using a two-dimensional finite-difference model for gas diffusion in the unsaturated zone. Mean PCH4 was greatest (1.56 Pa) in a pebbly-sand deposit 11.6 m below the land surface and 12 m from the waste, and generally decreased with increased horizontal distance from the waste. Mean PCH4 was least (0.07 Pa) at depth of 1.8 m below land surface, regardless of distance from the waste. PCH4 at the land surface averaged 0.17 Pa. Depth versus PCH4 profiles suggest consumption of both waste-produced and atmospheric CH4 in the upper unsaturated zone, presumably by methanotrophic microorganisms. Numerical simulations of methane movement support the consumption observation; inclusion of a term in the model for consumption of CH4 in the upper 2 m of the unsaturated zone resulted in simulated PCH4 within 30% of mean PCH4 at eleven of thirteen sampling locations. A similar fit of the data was obtained for only four locations when consumption was not considered. ?? 1989.
Additional Publication Details
Diffusion and consumption of methane in an unsaturated zone in north-central Illinois, U.S.A.