REMOVAL RATES OF SELECTED POLLUTANTS IN THE RUNOFF WATERS FROM A MAJOR RURAL HIGHWAY

The concentrations of cadmium, copper, lead, the organic compounds of lead and eight polycyclic aromatic hydrocarbons have been measured in surface drainage waters from a major rural highway in north-west England during a number of runoff events. The particulate phase (> 0.45-mu-m) contained > 90% of the inorganic Pb, approximately 70% of the Cu and approximately 56% of the Cd and the particulate-phase metal concentration profiles largely followed those of the suspended sediments. A "first-flush" effect was seen for the dissolved metals. A highly significant correlation was found between the length of the antecedent dry period and the amount of lead and dissolved copper removed during a runoff event but this was not found for the other pollutants. A simple regression model allows the reliable first-order approximation of lead concentrations and removal rates in the runoff waters to be made from the discharge rate and the length of the antecedent dry period. Budget calculations show that approximately 8% of the Pb, 5% of the organic lead and 3% of the PAHs emitted by vehicles are removed in the highway drainage waters.