150 



• Monitoring activity over the NL-91 and D/S mound complex in 1995 and 1997 

 continued to show mature and healthy benthic infaunal populations and sand-over-mud 

 layering over the mound. 



• The recolonization of the area by a diverse benthic community (Stages II and III), 

 representing a broad range of sensitivities, indicates that sediment toxicity and chronic 

 impacts are non-existent or unlikely. The response of the benthic community is a 

 direct indicator of potential for adverse effects and supports a conclusion that either 

 the UDM material was isolated by the surface sediments or the sediments were 

 conservatively classified during the regulatory process. Nonetheless, as a prudent 

 management measure, additional sediments were directed to this location in 1997- 

 1998 to thicken the cap, accompanied by periodic monitoring to assess any changes. 



• Additional cap material was placed over the central area in 1997-1998 as a 

 conservative management response to the relatively thinner cap coverage attained 

 during the project. A layer of new CDM (2-10 cm) was detected over the central 

 region of the mound using REMOTS® sediment-profile photography. 



• Normal rates of biological recolonization of the mound were observed in 1998. Areas 

 of new CDM had a combination of initial and advanced successional stages showing 

 the standard progression of recovery of the benthic community. 



5.3 USCGA Mound 



• The USCGA Mound was formed in 1994-1995 from 124,000 m 3 of material from the 

 U.S. Coast Guard Academy. Approximately 80,500 m 3 of CDM was placed over 

 43,500 m 3 of UDM creating a mound 420 m wide and 1 m high at the apex. The 

 mound overlapped and merged with the historical NL-TR Mound in the northeast 

 quadrant of the NLDS. 



• REMOTS® sediment profile results in 1995 indicated that the capped mound was 

 supporting a healthy benthic community. Some stations showed evidence of impact 

 from low dissolved oxygen or organic enrichment, but this was also seen at the 

 reference areas and is attributed to regional conditions of stress. 



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



