Determination of the environmental impact of consolidation induced convective transport through capped sediment

The presence of contaminated sediment poses a barrier to essential waterway maintenance and construction in many ports and harbors, which support 95% of US foreign trade. Cost effective solutions to remediate contaminated sed iments in waterways need to be applied. Capping is the least expensive reme diation alternative available for marine sediments that is unsuitable for o pen water disposal. Dredged material capping and in situ capping alternativ es, however, are not widely used because regulatory agencies are concerned about the potential for contaminant migration through the caps. Numerous studies have been conducted on the effects of diffusion through ca ps, however, there is a lack of experimental data documenting the effects o f consolidation induced transport of contaminants through caps. This study examines consolidation induced convective contaminant transport in capped s ediment utilizing a research centrifuge. In this study, consolidation induc ed convective transport was modeled for 7 h at 100 x g, which modeled a con taminant migration time of 8 years for a prototype that was 100 times large r than the centrifuge model. In this study, hydrodynamic dispersion was a f unction of the seepage velocity. And, advection and dispersion dominated th e migration of contaminants. Centrifuge model results were compared to an a nalytical solution for advection and dispersion. The advection-dispersion e quation demonstrated that the centrifuge test is a conservative estimate fo r predicting contaminant transport. In conducting sensitivity analysis of t he advection-dispersion equation to the centrifuge modeling, as hydrodynami c dispersion decreased, the time for contaminant breakthrough increased. Mo reover, as the sediment to water distribution coefficient increased, the co ntaminant concentration into the overlying water decreased. (C) 2001 Elsevi er Science B.V. All rights reserved.