An in-situ method to measure a soil's undisturbed pore gas radon concentration, diffusion length for radon and air filled porosity

Previous work has shown that for soils of insignificant permeability (soils with permeability less than about 10(-12) m(2)) the important soil parameters for characterizing radon mobility in the soil are the soil's steady-state pore gas radon concentration at depth (C-s), the soil's bulk diffusion length for radon (L) and the soil's air filled porosity (p(a)). Existing methods to measure these parameters have been based wholly or in part on measurements of soil samples taken to a laboratory for analysis, The drawbacks of this approach are twofold: (1) since soil structure can be quite heterogeneous, the sample may not have characteristics indicative of the site as a whole, and (2) since the parameters are dependent on soil structure and the soil structure of the sample may be changed in the process of acquiring the sample, one may be changing the parameters that one is trying to measure, These problems can be avoided by using a totally in-situ method to measure C-s, L, and p(a). This paper describes a totally in-situ method for simultaneously measuring the important soil parameters, based on measurements of the radon concentration as a function of time for the gas in a cavity in the soil.