1.2 Dredged Material Disposal Mounds 



In September 1997, Science Applications International Corporation (SAIC) 

 conducted a master bathymetric survey at the NLDS (Figure 1-2). The master bathymetric 

 survey provides a reference frame for locating the disposal and monitoring activities 

 conducted from 1991-1998. For each mound complex, the disposal history will be 

 described followed by a summary of monitoring activities. A timeline of all of these 

 activities (Figure 1-3) has been provided to summarize the events; details of the survey 

 methods are provided in Section 2.0. 



The September 1997 master bathymetric survey also marked the conversion from 

 the horizontal navigational reference system of the North American Datum of 1927 (NAD 

 27) to the North American Datum of 1983 (NAD 83) for all future bathymetric surveys 

 conducted at this site (see Methods section). 



1.2.1 Dow/Stonington and 1991-1992 Disposal Activity 



A series of buoy positions and disposal activities occurred between the fall of 1991 

 and spring of 1992 (Figure 1-3). These activities resulted in formation of a small, flat 

 mound complex (designated the New London-91 and Dow/Stonington mound complex) 

 that lies within the center of NLDS surrounded and protected by slightly higher mounds 

 (Figure 1-2). The surface of this mound complex shows little relief and has been 

 consistent in character throughout the six-year period covered by this report. Most of the 

 complex has an upper layer of sand mixed with shells and pebbles in some areas. This 

 surface has been rapidly colonized by a stable benthic community after each sequence of 

 disposal. 



The history of disposal within this area is complicated and needs to be described in 

 detail before presenting the survey results. The taut-wired buoy "NDA" was first deployed 

 for the 1991-1992 disposal season by SAIC on 26 September 1991 at coordinates 

 41° 16.239' N, 72°04.486' W (NDA #1; Figure 1-3). 



The sediments deposited at the NDA buoy were dredged from the Gwen Mor . 

 Marina in the Mystic River and Port Niantic, Inc. in the Niantic River. An estimated 

 barge volume of 5,700 m 3 of dredged material was deposited in close proximity to the 

 NDA buoy before it was struck and dragged off-station by a U.S. Navy submarine 

 transiting through NLDS (Appendix Al). 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



