701 
factor of 5,000. This would decrease the magnitude of the faster- 
settling fraction by reducing the extent of flocculation. However, 
it has not been determined what the effects of dewatering will have 
on settling rates, and no experiments to date have indicated whether 
turbulence generated in the dumping process will accelerate or 
hinder the flocculation processes. 
Estimates of sludge derived contaminant concentrations in 
sediment have been derived by calculating the flux of settling 
sludge into previously deposited sediment. Particles which settle 
at 10 m/day and thus reach the seafloor in 200 days would, con- 
servatively, be spread over a 10,000 km2 area. Once deposited, 
sludge, like natural particles, will be mixed into the sediment 
column by biological activity, a process called bioturbation. Data 
on rates of bioturbation in deep sea sediments indicate that a 
conservatively low rate constant for our calculations would be 
0.1 cm@/yr. 
Maximum concentrations of sludge components will occur at the 
sediment surface and will increase as long as dumping continues. 
After 100 years the incremental increases of trace element con- 
centrations due to sludge will be close to existing ambient concen- 
trations. Assuming no loss by dissolution as particles sink or 
degradation by bacterial action, the maximum concentrations of PCBs 
and PAHs after 100 years will be between 0.2 and 0.4 ug/g (dry 
weight), respectively (O'Connor et al., in press e). 
Dispersion of sludge dumped at the 106-Mile site would be 
sufficient to alleviate concern about contaminant, except for those 
substances in the faster-settling particles that are very highly 
concentrated in sludge relative to natural particles. It appears 
that after dumping has continued for many years, part of the 
deep-sea floor will be contaminated with PCBs and PAHs. There is 
not a good coastal analogue of this situation, because coastal 
areas contaminated with PCBs and PAHs also contain elevated levels 
of total organic carbon and a variety of inorganic contaminants. 
