Modeling contaminant transport through capped dredged sediment using a centrifuge

The presence of contaminated sediment poses a barrier to essential waterway maintenance and construction in many ports and harbors, which support 95% of U.S. foreign trade. Cost effective solutions to remediate contaminated sediments in waterways need to be applied. Capping is the least expensive remediation alternative available for marine sediments that is unsuitable for open water disposal. Dredged material capping and in situ capping alternatives, 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 caps, however, there is a lack of experimental data documenting the effects of consolidation induced transport of contaminants through caps. This study examines consolidation induced advective contaminant transport in capped sediment utilizing a research centrifuge. Centrifuge modeling simulates the increase in the gravitational acceleration (g) of a prototype, which is N times larger than the model, where N is gravitational acceleration factor. For contaminant migration, the time of transport in the model is inversely proportional to the square of the acceleration factor in the prototype. In this study, consolidation induced advective transport was modeled for 22.5 hours at 100-g, which modeled a contaminant migration time of 25 years for a prototype that was 100 times larger than the centrifuge model. Thus, advection and dispersion dominated the migration of contaminants. The centrifuge modeling results were compared to an analytical solution for advection and dispersion.