Diffusive transport of radon in a homogeneous column of dry sand.

To validate a model for radon transport in soil, measurements of diffusive radon transport under well-defined and controlled conditions have been made in a homogeneous column of dry sand with an air-filled volume on top. This volume simulates a crawl space. The measurements concern time-dependent diffusive transport with several different crawl-space heights and steady-state diffusive transport with different crawl-space ventilation rates. This study forms part of an extensive validation which will also cover more complex situations (e.g., advective transport, presence of pore-water). Properties of the sand that are presently being used in the radon transport model were determined from independent measurements. The comparison between model calculations and experimental results showed a good correspondence with maximum deviations of less than 10%.