Benchmark and application of the RAETRAD model

This paper reports on field measurements that were used to benchmark a simple new predictive correlation between soil gas permeability and soil grain size, moisture, and porosity. The correlation was incorporated with a previous diffusion correlation into the new RAETRAD code, that calculates radon generation and two-dimensional transport in soils, and radon entry into structures. RAETRAD generalizes the one-dimensional RAETRAN model, combining advective and diffusive radon transport with radon emanation, decay, absorption, and adsorption. RAETRAD calculations suggest 0.3 liter/minute normalized radon entry rate for slab-on-grade homes on low-permeability soils (<10-8 cm2), increasing to 7 liter/minute for sandy soils. Soil or fill properties in the first few feet dominate radon entry efficiency and limiting radium concentrations for prescribed indoor radon levels. For indoor radon concentrations of 2 pCi/liter, sandy soils may contain only 2-3 pCi/g radium compared to 10-20 pCi/g for more clayey soils