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3.0 MONITORING STUDIES 



The first experimental capping 

 operations were conducted simultaneously 

 with a monitoring program designed to 

 measure the short-term effectiveness of the 

 capping objectives (Appendix B). Initial 

 concerns regarding the long-term 

 environmental impact of capping 

 contaminated sediments resulted in both 

 periodic monitoring surveys and 

 investigations targeted to resolve specific 

 questions. The primary objective of the 

 capping operations was to isolate the 

 underlying contaminated material from the 

 ambient water column and local biota. 

 The ability of a sediment layer to 

 accomplish this goal depends on a variety 

 of physical, biological, and chemical 

 processes. These three characteristics, 

 although closely interrelated, were 

 monitored independently. 



The first indications that capping was, 

 indeed, a viable disposal method came 

 from precision bathymetric surveys 

 scheduled before disposal, after disposal of 

 mound material, and periodically after 

 capping. Results from these surveys 

 showed that dredged material could be 

 placed precisely and that the caps remained 

 in place after disposal. These bathymetric 

 surveys were closely followed by 

 biological and chemical monitoring that 

 confirmed the stability and integrity of the 

 sediment caps. 



Physical monitoring was designed to 

 observe the capped mounds for signs of 

 erosion or physical breaching and to 

 ensure complete cap coverage. Methods 



used have been primarily acoustic and 

 visual. Biological monitoring, consisting 

 of visual assessments and chemical 

 analyses of organisms, was conducted to 

 ensure that contaminants within the mound 

 were not having an adverse impact on the 

 benthic ecosystem. Recently, biological 

 monitoring procedures have focused on 

 efficient monitoring with accompanying 

 management response. Chemical 

 monitoring was initiated to confirm that 

 surficial sediments retained low 

 contaminant concentrations. Questions 

 concerning chemical mobilization from the 

 mound to the surface of the cap have been 

 addressed more recently (Section 4.0). 



3.1 Physical Characteristics 



The primary concerns raised by the 

 Scientific Advisory Committee related to 

 the physical stability of the capped 

 mounds. Successful disposal operations 

 alone could not determine the long-term 

 fate of a capped mound. Ability to 

 construct a coherent mound had to be 

 demonstrated. The committee also 

 questioned whether coarse-grained, sandy 

 material could be placed over fine-grained 

 sediments with higher water content; the 

 concern was that the impact of the sand 

 could disperse the underlying contaminated 

 material and limit the physical integrity of 

 the cap. 



3.1.1 Methods 



Morphology and short- and long-term 

 stability of capped mounds have been 

 examined by the DAMOS Program using a 

 variety of direct and indirect methods. 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



