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Isolation of Dredge Material 



1. Capping - One of the most common remediation solutions now 

 used (especially in New England) is capping, where clean dredge 

 material or other material is deposited in a thick layer over the 

 contaminated sediments to keep them in place. Dredge material 

 contaminated with heavy metals can be capped with lime or calcium 

 carbonate which binds the metals so they are not available to the 

 marine environment. Capping can work for sediments left in place 

 or for materials which have been dredged and deposited elsewhere. 



Capping is most effective where little sediment erosion 

 occurs such as on flat or depressed areas of the ocean floor. 

 Monitoring of the cap is needed to ensure its integrity, and 

 recapping may be necessary. Capping may not be effective in 

 deeper waters and costs may be prohibitive if much clean material 

 will need to be imported for the cap. On the whole, though, 

 capping is relatively inexpensive to use and is estimated to cost 

 approximately $9/cubic yard to use. This was the solution 

 recommended as part of the Newark Bay ocean dumping permit. 



2. Abyssal Plain Disposal - Not yet tested is the idea of 

 depositing contaminated sediments on the deep ocean floor on 

 geologically stable and ecologically barren areas known as 

 abyssal plains. Proponents of this technique argue that the 

 tremendous pressures at these depths may compact and immobilize 

 the sediments. In addition, they believe that sealife at this 

 depth is relatively scarce, and therefore contamination through 

 the food chain would be minimal. 



3. Borrow Pits - Often as a result of construction 



activities, subaqueous borrow pits are created in harbor areas 

 and on land. They can also naturally occur. These trenches can 

 be filled with contaminated sediments and then capped, if 

 necessary. Considerations involved in this method used in Lake 

 Ontario are accuracy of the placement and whether the sediments 

 can bear the weight of a cap. This is one alternative being 

 reviewed for the future management of contaminated dredge 

 material in the New York-New Jersey Harbor. 



4. Hardening - This treatment, which has been applied in 

 Japanese harbors, involves injecting a hardening agent (such as 

 Portland cement) into the sediments and stirring them up. The 

 sediment then solidifies and its contaminates pose a lesser 

 threat to the environment. This technique has been used with 

 dredge material, but can also be applied to sediments left in 

 place. Disadvantages of this technique are the resuspension of 

 contaminates after the stirring of the dredge material and the 

 very precise placement of the hardening agent required. In 

 addition, hardening works well with metals, but is less effective 

 with organic contaminates. The ultimate use of the hardened 

 material is a factor which must be considered, as the hardened 

 sediment can be sturdy enough for construction but continued 

 exposure to acidic c onditions can cause contaminates to escape. 



