Assessment of sediment contamination from pollutant discharge in surface waters

Based on theoretical considerations, the pollutant trapping efficiency (PTE) of a river section was introduced to assess sediment contamination from pollutant discharge. Under simplified assumptions, PTE can be calculated by the sedimentation of suspended particulate matter (SPM), the inflowing concentration of SPM and the solid-water partition coefficient K-d. Regarding a more complex field case, a one-dimensional flow and transport model was applied to a lock-regulated section of the Neckar River, Germany. Long-term simulations (1950-1994) were carried out (a) to analyse the temporal development of sediment contamination and (b) to quantify the dependence of the PTE of cadmium on K-d and the Damkoehler number, characterizing the time scale of the adsorption process with respect to the water residence time in the regarded river section. Sediment contamination by Cd shows a strong response to the decrease of Cd emission in the past. In the case of rapid adsorption, sediment contamination increases non-linearly with rising partition coefficient. This agrees qualitatively with the formula derived from theoretical considerations. At the measured kinetic adsorption rates, chemical equilibrium of solid-water partitioning is reached at low to moderate discharge, and sediment contamination in the river reservoir is determined by the hydraulic trapping of the polluted SPM. (C) 1998 IAWQ. Published by Elsevier Science Ltd.