currents apparently kept the inner portions of the channels scoured free of 

 invertebrates (U.S. Fish and Wildlife Service 1?77). 



Maintenance dredging will of course reipove or disrupt benthic organisms 

 and prevent establishrrent of mature communities (U.S. Army Corps of Engineers, 

 Buffalo District 1976). However, removal of polluted material and increased 

 water circulation as a result of maintenance dredging can sometimes improve 

 benthic communities (International Working Group 1975). 



ASSESSMENT OF IMPACTS OF DISPOSAL ALTERNATIVES 



Te rrestrial Disposal 



Terrestrial disposal of either confined or unconfined dredged material 

 must be accomplished with attention to the relationships between sediment 

 characteristics and subsequent land use (International Working Group 1975). 

 Sites must be carefully planned to control drainage and seepage, possible 

 groundwater contamination, effluent quality, and contaminant transfer to the 

 external environment by wildlife vectors. Unconfined disposal of grossly pol- 

 luted sediments is usually not considered acceptable (International Working 

 Group 1975). 



The literature concerning diked disposal areas in the Great Lakes indi- 

 cates that the effluent quality varies greatly (Sly 1977). The Chicago Dis- 

 trict of the Corps of Engineers has stated that large amounts of highly pol- 

 luted material are confined in disposal areas in the district but the sites 

 border water bodies that also are highly polluted (Harrison and Chisholm 

 1974). In at least one instance in Lake Erie, seepage through the dike did 

 not significantly affect water quality (U.S. Army Corps of Engineers, Buffalo 

 District 1969e). 



The length of detention time determines, to a great extent, the quality 

 of the effluent from diked disposal areas. These disposal areas have often 

 been ineffective in preventino the entry of contaminants into adjacent waters 

 (U.S. Army Corps of Engine^-s," Buffalo District 1969a, 1969b, 1976). Engineer- 

 ing Science, Inc. (1977) , ^und that only 0.4 mg/1 of oils returned over the 

 weir to the Cuyahoga River at Cleveland from material that was grossly contam- 

 inated with oil and greases (allowable discharge level was 10 mg/1). This 

 finding substantiates other studies which indicate that, given sufficient 

 retention time, oils and greases are not released from disposal areas in sig- 

 nificant quantities. A d'isposal site at Grand Haven, Michigan, had a short 

 retention time (less than 12 hr), the influent contained 39.5 mg/1 of oils and 

 creases and the effluent contained 11.5 mc/1, indicating inefficient removal 

 (Hoeppel et al. 1978, Table 8). 



High levels of PCEs were also being discharged, after a short detention 

 timic, from the Grand Haven site. The influent contained an average of 10.67 

 mg/1 and the effluent contained 2.55 mg/1. Based on a composite of evidence 

 from Grand Haven and six other nationwide land disposal sites, RGBs are appar- 

 ently associated with suspended solids and are efficiently removed from the 

 effluent when thorough settling occurs. At the Grand Haven site settling was 

 not complete and PCE removal, therefore, was incomplete. In contrast, some of 

 the other sites had good solids retention and consequently \jery efficient RGB 

 removal. An additional study in Seattle (Hoeppel et al. 1978) showed that 



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