170 



One particularly innovative program is being pursued in Great 

 Britain where microorganisms are used to immobilize and localize 

 metal ions from solution which are then separated with a high 

 gradient magnetic separation (HGMS) technique. This approach may 

 also be effective with polar organic compounds and is worthy of 

 further exploration. 



Although many of the sediment remediation strategies in Europe 

 parallel those being pursued in the U.S., differences in political 

 systems and the relationships between private industry, government 

 and public/environmental groups have enabled some European nations 

 to produce a long-range strategy with short-term tradeoffs. This 

 strategy uses specially-designed undersea disposal pits as near- 

 term solutions to manage dredged material while other 

 relocation/remediation alternatives are vigorously pursued in the 

 long-term. The common practice in the Netherlands is to reduce the 

 amount of contaminated material to a minimum by physical separation 

 of particles and to confine the most contaminated dredged materials 

 to double- lined land-containment areas or undersea pits, with the 

 more contaminated materials receiving greater levels of protection. 

 The same is essentially true for Belgium and Germany, with greater 

 emphasis on heavy metals in Belgium. Unlike Germany, Belgium and 

 the Netherlands do not treat large quantities of dredged material 

 regularly. Similarly, treatment projects in the U.S. have only 

 been conducted at the demonstration scale. 



Undersea Pit Disposal 



Undersea borrow pits have been used on an experimental basis in 

 Long Island Sound and the New England area as an alternative for 

 the disposal of contaminated sediments. This approach presumes 

 that contaminated sediments will be isolated and contained by a 

 clean sand cap and the pit walls and bottom. 



Data collected from capped disposal mounds as part of the Dredge 

 Area Monitoring System ;DAMOS) project indicate that no detectable 

 mobilization of trace metals has occurred over a 7-11 year period. 

 Although some mixing of contaminated and cap material was observed, 

 cores showed a distinct boundary between the two materials. Even 

 with consolidation, "he two sediments remained geochemically 

 distinct . 



Proper pit design and construction is important to the 

 effectiveness of this approach. Knowledge of the characteristics 

 and strengths of base materials used in pit construction, along 

 with depth and the impact of material disposed on the seaflcor is 

 necessary to account for settlement of the disposed material and 

 compression of the base material. Regardless of the type of pit 

 construction, the cap must prevent biological and physical 

 disturbance of the underlying dredged material to ensure that 

 contaminants are not remobilized. 



