Heavy metal transport from dredged sediment derived surface soils in a laboratory rainfall simulation experiment

Heavy metals in dredged sediment disposal sites may be transported through runoff and percolation. In the present study metal fluxes by runoff and per colation were determined under simulated rainfall at a slope of 19% and a r ainfall intensity of approximately 40 mm h(-1). These circumstances corresp ond to half the mean annual erosivity of rain under Belgian weather conditi ons. Surface runoff and percolating water samples were analysed for suspend ed solids, total dissolved carbon and Cd, Cr, Cu, Ni, Pb and Zn. Runoff rat e and sediment yields were highest for a silt loam sediment, characterised by a low clay and organic matter content. Metal concentrations in runoff an d percolating water varied widely between the sediments studied and were re lated to the total metal content in the sediment. In runoff and percolating water from the contaminated sediments, metal concentrations strongly excee ded the Netherlands A reference values for ground water quality. Very high metal fluxes were observed for the recently oxidised dredged sediment. Meta l transport per unit surface area through percolating water was from two to more than twenty times greater than that in surface runoff.