48 



contamination or from nonspecific forms 

 of environmental degradation, does not 

 prove that the capping operations 

 successfully contained all of the 

 contaminants. However, it is clear from 

 these data that any undetected release did 

 not have immediate or widespread 

 consequences to the benthic community 

 structure or significantly accumulate in the 

 tissues of suspension-feeders tethered near 

 the bottom. 



Subsequent biological samplings of the 

 capped disposal mounds have included 

 benthic grabs on an intermittent basis for 

 community analysis and bioaccumulation 

 (SAIC 1989). The primary emphasis has 

 been placed on recolonization 

 characteristics as monitored through the 

 use of REMOTS® technology. The 

 disposal of dredged material capped with 

 natural sediments is analogous to the burial 

 of a section of the community by a layer 

 of new habitat. By following the 

 processes associated with recolonization 

 (bioturbation, oxygenation, succession), it 

 is possible to glimpse an integrated picture 

 of the biological response to disposal. 

 This picture may lack specifics of 

 contaminant bioaccumulation but, unlike 

 the mussel data, can contain important 

 clues to the processes affecting the 

 response of the community. Most 

 importantly, effective management of 

 capped mounds requires timely information 

 on the relative health of the biological 

 communities developing at the surface. 

 Only with rapid, predictive monitoring 

 techniques can remedial actions be applied 

 efficiently if capping operations are not 

 successful. 



3.2.2 Sediment Profile Imaging 



Since 1982, the REMOTS® sediment- 

 profile camera has been included routinely 

 in DAMOS surveys of the CLIS capped 

 disposal mounds (Appendix C). In 

 addition to physical-chemical evaluations 

 such as grain size and surface boundary 

 roughness estimates, REMOTS® 

 photographs provide a visual indication of 

 the successional status of the benthic 

 community, allowing an assessment of the 

 recolonization rates of dredged material 

 deposits. The most commonly documented 

 successional stages in the DAMOS 

 Program are Stage I (very small 

 polychaetes and amphipods) and Stage III 

 (larger burrowing macrofauna). 



Evaluations of infaunal successional 

 stages are combined with measured 

 physical parameters (e.g., the redox state, 

 presence of methane gas in the sediment, 

 etc.) to develop a quantitative measure, or 

 index, of disturbance or "stress." This 

 calculated Organism-Sediment Index (OSI) 

 is believed to provide a sensitive indicator 

 of the response of the benthic community 

 to a variety of stresses, including exposure 

 to contaminated sediment (Rhoads and 

 Germano 1986). 



REMOTS® observations can be used to 

 document the long-term biotic health of a 

 capped mound. One of the advantages of 

 reviewing the historical DAMOS data is 

 that the applicability of environmental 

 monitoring approaches can be appraised. 

 For example, time-series plots of OSI 

 values at the CLIS mounds and the CLIS 

 reference station show strikingly clear 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



