and second, isolating potentially harmful 

 material from contact with ocean biota and 

 humans. 



A variety of special "handling" 

 techniques were also introduced to 

 minimize material losses during dredging 

 operations and to maximize long-term 

 containment of sediments and associated 

 contaminants at disposal sites. Clamshell 

 buckets and hopper barges routinely are 

 used to increase the compaction of the 

 sediments (cohesion), thereby reducing the 

 potential for loss of sediment during 

 dredging and transport. Additionally, the 

 use of highly accurate electronic 

 positioning systems and taut- wired, 

 moored buoys for precise disposal of 

 material have proved particularly 

 successful. 



For the purposes of this monograph, 

 the term "mound" will be used to describe 

 the deposit formed by the disposal of 

 contaminated dredged material which is 

 subsequently covered with cleaner material 

 (Figure 1-1). The term "cap" will be used 

 to describe that subsequent deposit formed 

 by the disposal of relatively cleaner 

 dredged sediments. The term 

 "contaminant" will be used to describe 

 those inorganic and organic elements and 

 compounds, either natural or 

 anthropogenic, which, in high enough 

 concentrations, may pose a human health 

 threat. It is important to emphasize that, 

 for brevity, the term contaminant is used 

 here to describe all analyzed components, 

 regardless of their concentration. 



1.4 Record of Capping in New 

 England 



The New England Division (NED) has 

 conducted more shallow-water capping 

 activities than any other USACE division. 

 This experience has generated a distinct 

 evolution of techniques and an approach to 

 monitoring that is unique within the Corps, 

 attracting national attention and interest 

 (NRC 1989). Monitoring results, managed 

 through the DAMOS Program, have 

 consistently shown these caps to be stable 

 with no evidence of contaminant release. 

 Capped mounds have withstood the 

 passage of hurricanes, and so can provide 

 valuable information on the stability of cap 

 material and mobility of contaminants over 

 time. This record, including mistakes, 

 lessons learned, and successes, can help 

 guide future activities in New England and 

 throughout the world. Pressures to use the 

 open ocean for disposal of contaminated 

 dredged material have increased, and many 

 areas of the United States may need to 

 implement capping in the future. 



The use of clean sediment layers to 

 provide barriers limiting leachate 

 migration and to control surface erosion of 

 waste deposits has been a standard practice 

 at municipal and industrial disposal sites 

 on land for many years. However, no 

 planned capping project took place at an 

 underwater site in the United States until 

 1979. Capping projects prior to that time 

 were "de facto" operations in which burial 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



