better than 99.8% of PCBs can be removed after only a short retention time by 

 the use of flocculants. 



Other potential pollutants that were not efficiently removed at the Grand 

 Haven site included DDE and several forms of nitrogen and phosphate. Pollu- 

 tants that were efficiently removed included DDD, DDT, manganese, zinc, cad- 

 mium, copper, nickel, lead, chromium, vanadium, and arsenic. Mercury was not 

 monitored. Apparently, DDE is associated with fine clay particles while DDD 

 and DDT are associated with larger particles and thus are more readily removed 

 by settling (Hoeppel et al . 1978). Studies in Lake Erie and Lake St. Clair 

 have shown mercury to be associated with fine particles (Mudrock 1979). Plants 

 in Lake St. Clair showed limited uptake of mercury. Highest concentrations 

 were found in the roots. 



Evidence from Grand Haven and other sites (Hoeppel et al . 1978) indicates 

 that contaminants in freshwater areas behave like contaminants in saline wa- 

 ters. However, settlement may be quicker in salt water due to the floccula- 

 tion inducement by the salt; also the buffering capacity of salts may render 

 certain contaminants less potent. 



Island, Fastland, or Beach Disposal 



Dredged material in the Great Lakes is often used to create islands or 

 fasti ands that become a part of the land mass, and for beach nourishment. 

 General principles discussed in Part III - Coastal Waters should generally 

 hold true for the Great Lakes and the reader is referred to that section. 



Wetland Disposal 



References on impacts of disposal on wetlands in the Great Lakes were not 

 found. It is assumed that wetland disposal is rare in the Great Lakes area. 



Nearshore Disposal 



The greatest concern with disposal of dredged material in the Great Lakes 

 has been the question of impact of aquatic disposal. Both short- and long-term 

 impacts have been areas of concern. 



Sly (1977) noted that disposal in shallow waters, which are strongly 

 influenced by winds and waves, causes more resuspension of particles than dis- 

 posal in deep water. Resuspension of particles will often lead to increased 

 levels of nutrients and potential contaminants in the water column. Also, the 

 shallow nearshore zone is usually more productive and of greater importance 

 for spawning and nursery purposes than the deepwater portions of the Great 

 Lakes. 



In a disposal area outside the breakwater of Cleveland Harbor, the post- 

 dump bottom sediments of the disposal area were characterized by increases in 

 the same chemical constituents that were found in the harbor (U.S. Army Corps 

 of Engineers, Buffalo District 1969c). Background levels in areas surrounding 

 the disposal area were also relatively high. Disposal areas in the St. Marys 

 River were characterized by unstable and constantly shifting sediments. Macro- 

 invertebrate numbers were greatly depressed (U.S. Fish and Wildlife Service 

 1977). 



77 



