Chunhua Liu, Raveendra V. Ika, James P. Shine, Timothy E. Ford

Environmental Science and Engineering
Harvard School of Public Health
Boston, MA 02115

Theoretical simulations suggest that capping is very efficient in preventing contaminant transport to the overlying water. For example, theoretical calculations based on molecular diffusion suggest that it would take more than 900 years for trichlorophenol to break through a 45 cm cap.

In laboratory studies, no metal (Ag, Cd, Cr, Cu, Ni, Mo, Pb, Zn) transport into capping material occurred in simulator cells over a six month period. Hence, in the absence of wave action, the sedimentation rate in depositional areas may be sufficient to prevent contaminant breakthrough. However, advective transport of contaminants through capping material is likely to be highly dependent on seepage rates and chemistry of groundwater, yet submarine groundwater discharge (SGD) rates at near shore capping sites are seldom evaluated. A series of capping simulator cells were therefore established with different groundwater chemistries and flow rates. Preliminary data suggests that advective transport of contaminants is highly significant under conditions of SGD. SGD may significantly effect capping efficiency and, therefore, greater emphasis on groundwater hydrology is critical before selection of near shore capping sites for disposal of contaminated sediment. This paper will present data on contaminant transport under conditions of SGD and the influence of different groundwater chemistries.