1.0 INTRODUCTION 



1.1 Background 



Coastal waters, especially harbor areas, 

 have been used directly and indirectly for 

 the disposal of industrial waste. This 

 waste, and the contaminants associated 

 with it, ultimately has been deposited in 

 marine sediments, most frequently within 

 or near harbors and industrialized 

 coastlines. A working definition of 

 contaminated sediments is "those that 

 contain chemical substances at 

 concentrations which pose a known or 

 suspected environmental or human health 

 threat" (NRC 1989). 



Research efforts continue to unravel 

 the impact of contaminated sediments on 

 marine ecosystems and the contaminant 

 pathways from marine sediments through 

 the food chain to eventual consumption by 

 man. Policy decisions regarding the 

 removal or isolation of existing 

 contaminated sediments are complex. 

 There are substantial risks and costs 

 associated with any action, as well as with 

 the choice of no action. Removal of 

 contaminated sediments introduces 

 secondary effects including sediment 

 resuspension and potential remobilization 

 of contaminants. These removed 

 sediments must be chemically or 

 biologically treated, or relocated in an area 

 which minimizes the impact on the local 

 ecosystem. 



Leaving the sediment in place is not 

 without risk or cost. Contaminated 

 sediments generally accumulate in 



depositional zones and will eventually be 

 buried. If buried by sufficient amounts of 

 noncontaminated sediments, the 

 contaminants will be isolated and will no 

 longer pose a health risk (NRC 1989). 

 However, until they are covered, in-place 

 sediments may act as a long-term "source" 

 of contaminants to nearshore environments 

 as they are intermittently disturbed by 

 waves generated by storms and vessel 

 traffic. These nearshore environments 

 generally provide the greatest risk to 

 human health. 



In the event that it becomes necessary 

 to remove coastal sediment, as in the case 

 of dredging of navigational channels, a 

 cost-effective management strategy is 

 required. Risk evaluations of dredged 

 sediment have traditionally used elutriate 

 and bioassay analyses in order to classify 

 the sediments as contaminated or 

 noncontaminated. Approximately 95% of 

 the total volume of dredged material is 

 considered noncontaminated (Palermo et 

 al. 1989). 



If the sediment to be removed is 

 considered to be contaminated, the 

 disposal alternatives are limited. 

 Alternatives for contaminated dredged 

 material are containment options 

 (subaqueous or upland) and treatment. 

 Unresolved containment issues include the 

 availability of space (especially on land) 

 and the degree of isolation that can be 

 achieved. Biological, chemical, and 

 physical treatment methods are being 

 developed, and each has its own 

 advantages and disadvantages. Treatment 

 is used for highly contaminated sediments, 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



