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 vapourphase 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 UK Air Quality Standard).