Contamination of indoor air by toxic soil vapours: a screening risk assessment model

A simple steady-state model is derived for estimating the concentration of vapour-phase contaminants in indoor air, given the contaminant concentration in the soil. The model includes the key mechanisms of transport and dispersion—contaminant partitioning into the soil-vapour phase, molecular diffusion, suction flow, and ventilation rate. It is shown that indoor air concentrations are largely controlled by two variables: soil permeability, and the half-life for contaminant removal from soil. A worked example shows the effect of these two variables on the concentration of benzene in soil that would give rise to a concentration of benzene in indoor air of 5 ppb (the recently proposed U.K. Air Quality Standard).