108 



Thames River channel, yielding a 1.82:1.0 CDM to UDM ratio, was placed over the Seawolf 

 Mound area. These materials consisted of new work material (largely glacial clay) and 

 maintenance material from the outer channel (largely fine sand). In addition, a total of 

 15,490 m 3 of CDM from Mystic River and Venetian Harbor were deposited at the NDA 95 

 buoy, which also contributed to the Seawolf Mound. The resulting Seawolf Mound is a flat 

 area east of the NL-RELIC Mound with a small oval apex. 



4.2.1 Topographic Changes of the Seawolf Mound 



The topographic profile of the Seawolf Mound at the completion of the project 

 showed a large, flat plateau (600 m diameter) with a small central apex with minimum 

 depths of 16 m (Figure 3-5). Postcapping surveys showed that consolidation of the deposit 

 followed the typical pattern for dredged material disposal mounds, with rapid consolidation 

 in areas of the thickest material (e.g., Poindexter-Rollings 1990; Silva et al. 1994). 

 Consolidation continued in the period between the first postcap survey (February 1996) and 

 the follow-up September 1997 survey (Figure 3-9). A small area of CDM on the western 

 side of the mound may have remolded, resulting in a slight increase in mound height 

 adjacent to an area of apparent consolidation. Consolidation analysis also revealed isolated 

 areas of apparent consolidation and accumulation. These small isolated fluctuations are a 

 product of slight variations in survey conditions (survey artifacts) and do not represent 

 changes in seafloor conditions (see Section 2.1.3). 



Sediment core and REMOTS® sediment profile data were evaluated to verify that 

 CDM covered the entire UDM deposit and provide more detail than possible with 

 bathymetric techniques (Section 4.2.4). REMOTS® images at Stations 150W and 300W 

 (the areas with apparent remolding) indicated the presence of glacial gray clay and brown 

 sand typical of the Seawolf CDM. The gray clay (Gardiners clay) is the product of 

 improvement dredging that removed glacial lake clays deposited beneath the estuarine 

 deposits in the Thames River. It is a stiff olive-gray to blue-gray clay that is very distinctive 

 in cores and REMOTS® images. 



Results from the July 1998 survey indicated that topographic changes after 

 September 1997 were greatly reduced, consistent with the equilibrium phase of dredged 

 material consolidation (Figure 3-12). The pattern of consolidation measured at other open- 

 water disposal mounds in Long Island Sound predicts that the Seawolf Mound will remain 

 in its current configuration with minor resuspension of the surface sediments (Section 

 4.2.3). In the event of a large storm event in the Sound, follow-up confirmatory 

 bathymetric data should be collected. 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



