Heavy Metal and PAH Concentrations in Highway Runoff Deposits Fractionated on Settling Velocities

The correlation between settling velocity and associated pollutant concentrations is of major importance for best management practice in designing, redesigning, or evaluation of the efficiency of existing pond facilities for retaining unwanted pollutants. The prospect of this note is to state the relationship between the settling velocity of the runoff particles and the corresponding metal and polyaromatic hydrocarbon (PAH) concentration directly instead of dealing with two unknowns-the density and the shape of a single particle fraction in a settling velocity calculations. The measurements show that the highest cadmium, chromium, zinc, and nickel concentrations is associated with the most slowly falling particles and the lowest concentration associated within the faster falling fraction. This tendency is not clear for some of the sediments due to high content of organic matter and clearly not for lead and copper and there is no significant correlation between PAH concentration and settling velocity. The largest mass of metals and PAH within each pond can be found on the particle fraction with a settling velocity of 5.5-2.5 mm/s.