Modeling lateral gas transport in soil adjacent to old landfill

Lateral migration of landfill gases in soils surrounding old (closed) munic ipal landfills can lead to explosion hazards and damage to vegetation. Land fill gas production and migration is controlled by microbial activity and s oil physical properties such as gas lair) permeability, gas diffusivity, an d atmospheric pressure variations. Gas diffusivity and air permeability wer e measured on undisturbed samples collected at an agricultural field adjace nt to an old Danish municipal landfill. Empirical expressions for predictin g gas diffusivity and air permeability from soil-water content were fitted to the data. An empirical expression for calculating methane oxidation rate as a function of soil temperature was developed using site-specific measur ements of methane oxidation rate. The transport and degradation parameter e xpressions were incorporated into a numerical model for simulating landfill gas transport, using soil-water content, temperature, and soil organic mat ter content as measured input parameters (functions of time and soil depth) . Previous measurements of landfill gas (CO, and CH,) concentrations and fl uxes in the agricultural field soil conducted over a period of one year wer e used to calibrate the gas transport model using methane oxidation rate, l andfill gas pressure, and wind-induced dispersion as fitting parameters. Th e model was subsequently tested against independent concentration and flux data (not used in the model calibration). This yielded a prediction accurac y similar to that found during the calibration. The model was used to evalu ate the sensitivity of landfill gas concentration and flux with respect to a set of governing parameters. The results of the sensitivity analysis indi cated that landfill gas migration in the field soil was most sensitive to a ir permeability and soil-water content. Methane oxidation rate and atmosphe ric pressure variations had some effects, especially on the gas Bur, wherea s gas diffusion was not important.