Numerical modelling of radon-222 entry into houses: an outline of techniques and results

Numerical modelling is a powerful tool for studies of soil gas and radon-222 entry into houses. It isthe purpose of this paper to review some main techniques and results. In the past, modelling hasfocused on Darcy flow of soil gas (driven by indoor-outdoor pressure differences) and combineddiffusive and advective transport of radon. Models of different complexity have been used. Thesimpler ones are finite-difference models with one or two spatial dimensions. The more complexmodels allow for full 3D and time dependency. Advanced features include: soil heterogeneity,anisotropy, fractures, moisture, non-uniform soil temperature, non-Darcy flow of gas, and flow causedby changes in the atmospheric pressure. Numerical models can be used to estimate the importance ofspecific factors for radon entry. Models are also helpful when results obtained in special laboratory ortest structure experiments need to be extrapolated to more general situations (e.g. to real houses oreven to other soil-gas pollutants). Finally, models provide a cost-effective test bench for improveddesigns of radon prevention systems. The paper includes a summary of transport equations andboundary conditions. As an illustrative example, radon entry is calculated for a standard slab-on-gradehouse.