Geology and occurrence of radon

The accumulation of radon indoors is commonly due to movement of radon from adjacent soil and rock into a building foundation through joints, utility openings, cracks, or porous block walls. When air pressure inside the building is lower than that in the soil, pressure-driven flow of radonbearing soil gas can occur (see Chapter 2). Whether or not an indoor radon problem results depends on: (1) the radium concentration in the soil and underlying rock, (2) the ability of radon to escape from the solid material holding the parent radium, and (3) the ability of radon to move through the rock and soil fractures and pores.