Significant concentrations of PAHs and hydrocarbons were recorded in soil, beneath an asphalt cover. The site had not received any significant inputs from internal combustion vehicles and hence the contaminants would appear to have originated through leaching from the asphalt surface. PAH concentration in the soil samples was positively correlated with the moisture content at the site. A direct logarithmic relationship could be demonstrated between soil content of a particular PAH and molecular properties such as water solubility. The ratios between individual PAH concentrations at sites which had undergone different degrees of leaching also showed a linear logarithmic relationship to molecular descriptors such as connectivity index. It is suggested that a significant amount of PAH can enter the environment through leaching from asphalt surfaces. At least some of the roadside PAH contamination probably results from this pathway, in addition to deposition from exhaust fumes.