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5.0 SUMMARY AND 



RECOMMENDATIONS 



Based on monitoring results from the 

 capped dredged material disposal mounds 

 in the DAMOS Program, there has been 

 no evidence of physical or chemical 

 breaching of the cap. The history of 

 DAMOS illustrates that capping is a viable 

 method of contaminated dredged material 

 management. Capping success depends on 

 several factors that have been learned 

 through experience over the course of the 

 DAMOS Program. Quality control during 

 every phase of capped mound formation is 

 essential, as is effective monitoring. 



The first capped mound projects, both 

 Stamford-New Haven North and South 

 (STNH-N and STNH-S) and Cap Site 2 

 (CS-2) were clearly the most successful of 

 the early capped mounds. Bathymetric 

 and REMOTS® data showed them to be 

 thickly covered with capping material from 

 the center to the flanks. Successful point- 

 dumping of mound material and 

 subsequent strategic placement of capping 

 material at the top and flanks of the mound 

 were accomplished with both a taut-wired, 

 moored buoy and accurate navigational 

 controls. 



Long-term stability of the capped 

 mounds has been tested during at least 12 

 years of monitoring and the passage of 

 three hurricanes. There is some evidence 

 that STNH-S may have experienced some 

 erosion as a result of Hurricane David in 

 1979, although the hurricane's passage was 

 coincident with the predicted exponential 

 compaction phase. Additionally, recent 



coring data showed that a thick (at least 

 1.4 m) cap remained at this, and other, 

 cored mounds. However, it is 

 recommended that capping operations be 

 planned to avoid peak storm periods so 

 there is time for natural settlement and 

 compaction. 



Generally, Long Island Sound capped 

 mounds have continued to show normal 

 biological recolonization rates in 

 subsequent monitoring. Sediment 

 chemistry data showed that, after capping, 

 surface sediment contaminants were at or 

 below background concentrations. Recent 

 coring data showed sharp visual and 

 chemical boundaries in many of the cores. 



More significantly, examination of the 

 historical record of capped mounds that 

 were not as successful provides equally 

 important information for dredged material 

 managers. For example, accurate 

 placement of dredged sediments is less 

 reliable without the use of both a taut- 

 wired, moored buoy and precise navigation 

 (partial offset of cap and mound occurred 

 at CS-1 due to the lack of these two 

 controls). 



The Mill-Quinnipiac Rivers mound 

 (MQR) provided perhaps the best evidence 

 for the need to control operational factors 

 and to monitor these mounds effectively. 

 More recently, the MQR mound was used 

 to test the tiered monitoring approach 

 developed for DAMOS. Biological 

 monitoring at MQR showed abnormal 

 recolonization rates relative to the other 

 CLIS sites. The disposal episodes, 

 including sediments from the Mill and 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



