ASSESSMENT OF SEDIMENT AND POREWATER AFTER ONE-YEAR OF SUBAQUEOUS CAPPING OF CONTAMINATED SEDIMENTS IN HAMILTON HARBOR, CANADA

In this manuscript, we present data from a demonstration in situ cappi ng site (100 m x 100 m) in Hamilton Harbour, Lake Ontario, Canada. A l ayer of clean medium to coarse sand with the average thickness of 35 c m was placed at the site in the summer of 1995. Concentration of Zn, C r, and Cd in the original sediments reached values over 6000, 300 and 15 mu g/g, respectively. The predicted consolidation of the uppermost one meter of sediment was about 14 cm, which was in good agreement wit h values obtained from comparisons of moisture content values of pre-c apping and post-capping cores. A thin layer of fresh moderately contam inated sediments has started to develop on the top of the cap. In gene ral, the concentrations of elements were greater in porewater than in the overlying water, e.g., the concentration of Fe and soluble reactiv e phosphorus were 1000 times, and those of Mn 100 times greater. There was a significant reduction in the vertical fluxes of all the trace e lements after the capping of the contaminated sediments. (C) 1998 IAWQ . Published by Elsevier Science Ltd.