Modeling Radon Entry into Florida Houses with Concrete Slabs and Concrete-Block Stem Walls: Fid-Bau Portal

Modeling Radon Entry into Florida Houses with Concrete Slabs and Concrete-Block Stem Walls

K. L. Revzan / W. J. Fisk / R. G. Sexton

The report discusses results of modeling radon entry into a typical Florida house whose interior is slightly depressurized. The model predicts that the total radon entry rate is relatively low unless the soil or backfill permeability or radium content is high. For a fixed soil permeability, the total radon entry rate may be reduced by a factor of 2 or more by (1) decreasing the backfill permeability, (2) making the stem wall impermeable and gap-free (possibly by constructing a one-piece slab/stem-wall footing), or (3) increasing the pressure in the interior of the stem wall (by ensuring that there is a large pressure drop across the slab/stem-wall gap). The part of the house included in the model consists of a concrete slab supported by a permeable concrete-block stem wall and a concrete footing. A region of undisturbed soil extending 10 m beyond and below the footing is also included. The Laplace equation, resulting from Darcy's law and the continuity equation, and the mass-transport equation are solved using a steady-state finite-difference model to determine the pressure and radon concentration fields in the soil. The house and soil are represented as cylindrically symmetric.