PART II 



CHARACTERISTICS OF DREDGED MATERIAL 



The composition of dredged material from a particular site affects its 

 pollution potential as well as the potential for habitat development or other 

 beneficial uses. Dredged material can be classified by grain size and may 

 range from clay to sand (or even rocks). The finer grain sizes have a greater 

 ability to adsorb and retain contaminants. The grain size also partially de- 

 termines the suitability of dredge material for construction or fill material 

 and for habitat development. According to Boyd et al . (1972), most dredged 

 material is classified as mixed sand and silt. Some basic differences between 

 the material derived from the construction of new channels and material deriv- 

 ed from maintenance dredging are discussed in the following paragraphs. 



MATERIAL FROM NEW CHANNEL DREDGING 



Physical Characteristics 



Sediments dredged from new channels consist of material that was deposit- 

 ed by natural processes, often before the appearance of modern man. The sedi- 

 ments may be clay, silt, sand, or rock and often layers of more than one type 

 may be encountered. The presence or absence of organic matter is determined 

 by the mode of sediment deposition. 



Dredged material from new channels or "new work" projects often has chem- 

 ical and engineering properties which create fewer environmental problems than 

 material from maintenance projects (Boyd et al . 1972). 



Contaminants 



Except for the top layer of sediments, contaminants are normally not pre- 

 sent in material removed from new channels. However, natural levels of heavy 

 metals will be present and, in some instances, the effluent from these mate- 

 rials could exceed water quality criteria (Gustafson 1975). 



Nutrients 



Nutrient levels in material from new channels vary widely depending on 

 the origin and nature of sediments. 



Potential for Productive Uses 



The value of dredged material for productive uses varies because of 

 variations in composition, particularly grain size, of the material. A lack 

 of organics is an asset in construction and fill uses, but is disadvantageous 

 (but not critical) in marsh or other types of habitat development. The absence 

 or low level of contaminants in material from new channels is also a definite 

 advantage; presence of contaminants can rule out many beneficial uses. 



MATERIAL FROM MAINTENANCE DREDGING 



Material removed during maintenance dredging of navigation channels is 

 an accumulation of detached soil particles which have been transported by wind 



