of bottom currents and storm-generated waves, sediment mounds at NLDS are developed in 

 a broad, flat manner, maintaining a minimum water depth of 14 meters. This minimum 

 depth also allows for the safe passage of deep draft Navy and commercial vessels transiting 

 through the disposal site (NUSC 1979). Presently, there are 10 discernible mounds within 

 the boundaries of the disposal site (Figure 1-2). 



Follow-up monitoring surveys of three capped mounds (New London 1991 and 

 Dow/Stonington Mound Complex, Seawolf Mound, and USCGA Mound) were conducted at 

 the NLDS in August 2000. All three of these mounds were formed and capped prior to 1997. 

 The development of each mound and recent survey activities are described briefly in the 

 following sections. 



1.1 NL-91 and D/S Mound Complex 



Disposal activity at NLDS during the 1991-1992 disposal season resulted in the 

 formation of the NL-91 and D/S Mound Complex. Dredging projects in the Mystic and 

 Niantic Rivers, as well as in Stonington Harbor and at the Dow Chemical Company, 

 provided 36,000 m^ of UDM and 59,300 m^ of CDM for use in a subaqueous capping project 

 (SAIC 2001a). The sediments were sequentially dredged and placed on the NLDS seafloor 

 in an effort to develop a capped disposal mound. 



Depth difference calculations performed as part of the post-cap monitoring effort 

 indicated that cap material thickness over the initial UDM deposit was somewhat less than 

 anticipated. While sediment-profile photographs obtained in 1 992 and 1 995 indicated a 

 stable and progressing benthic community had rapidly recolonized the capping layer 

 (comprised of fine sand and shell), it was recommended that additional CDM be placed at 

 specific points over the capped mound to further isolate the UDM from the benthic 

 environment (SAIC 2001a). 



Nearly 7,000 m^ of additional CDM was placed over the NL-91 and D/S Mound 

 Complex during the 1997-1998 disposal season and documented in the July 1998 sediment- 

 profile imaging survey. During the 1998-1999 disposal season, a total barge volume of 

 22,210 m^ CDM was placed in the northern and central regions of the mound complex 

 (Appendix A). An additional 1,375 m^ of CDM was deposited over the mound from 16 to 19 

 May 2000 to continue augmentation of the cap. The topography of the NL-91 and D/S 

 Mound Complex was last surveyed in September 1 997 as part of the master bathymetric 

 survey of the entire disposal site. 



Monitoring Cruise at the New London Disposal Site, August 2000 



