The paper discusses a simplified model for soil-gas transport through soil surrounding the substructure of a house. The model provides the ability to answer, in semi-quantitative terms, such fundamental questions as: (1) What role does diffusion play in transporting radon to the house/soil interface, where pressure-driven flow tends to dominate the process of entry into the house. (2) Do active subslab depressurization mitigation systems significantly increase the rate of emission of radon into the ambient air. (3) At what flow rate through the subslab depressurization system does dilution of the radon in the soil gas contribute significantly to the performance of the mitigation system. Simplifying assumptions about the distribution of entry routes and driving forces are used to relate indoor air radon levels to soil characteristics and to dynamics within the house. Preliminary validation of the model predictions consists of demonstrating reasonable values for indoor radon concentrations. While it is quite possible to formulate a fairly rigorous mathematical model to describe radon transport through soil, such a model would require rather complex numerical solutions that would be time consuming and expensive to evaluate. Numerical solutions are also cumbersome for evaluating both the relative importance of the individual mechanisms and the appropriateness of alternative boundaries.

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