INSITU MEASUREMENT OF GAS-DIFFUSION COEFFICIENT IN SOILS

A method for determination of the gas diffusion coefficient of soils without disturbing the natural state of the soil was developed. The method was based on the theory of radial diffusion of a finite quantity of gas into a semi-infinite porous medium. Needles were inserted into the soil through which O2 was injected. The change of concentration of the injected O2 was determined by gas chromatography through the same needle after increasing periods of time. A least square fit between the measured O2 concentrations and that of the theoretical values was conducted to find the best fit value of the diffusion coefficient. The diffusion coefficient determined by the proposed method was used to calculate the flux of CO2 in field soils. The flux so calculated was compared to that measured from the field with good agreement. The method was used in several different field soils and conditions to determine the diffusion coefficients.