The paper refines and extends an earlier study--relating to the design of optimal radon mitigation systems based on subslab depressurization--that suggested that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained between two impermeable disks. It also shows that subslab air flow is most likely to be turbulent under actual field situations in houses with subslab gravel beds, while remining laminar when soil is present under the slab. It discusses the physical significance of a model and derives simplified closed-form equations to predict pressure and flows at various distances from a single central depressurization point. A laboratory apparatus was built to verify the model and experimentally determine the model coefficients of the pressure drop versus flow for commonly encountered subslab gravel materials. These pressure drop coefficients can be used in conjunction with the simplified model as a rational means of assessing subslab connectivity in actual houses, which is an important aspect of the premitigation diagnostic phase. Preliminary field verification results in a house with gravel under the basement slab are presented and discussed.