70 



between the precap and interim cap surveys of the CLIS 94 mound. The pocket of central 

 consolidation was responsible for a large percentage of a 121,300 m 3 shortfall in the mass 

 balance of material. However, agreement between the reported barge volume and the 

 volume detected acoustically improved by tracking the volume through the four phases of 

 mound development. 



Physical and biological indicators of overall benthic community health suggest the 

 CLIS 94 mound is recovering faster than expected. A few stations displayed signs of low 

 dissolved oxygen; however, the majority of the mound was characterized with moderate to 

 deep RPDs and evidence of Stage III organism activity. As a result, the overall OSI value 

 of 5.23 suggests the CLIS 94 mound should reach full recovery (RPD >6) in the next two 

 years. 



Conversely, the FVP mound, composed of an uncapped UDM deposit, is 

 continuing to show signs of low habitat quality with shallow RPDs and low OSI values 

 over the center of the mound. Although the regional hypoxic event may have contributed 

 to the problems at FVP, the mound has traditionally been more susceptible to benthic 

 disturbances and slower to recover, relative to other project mounds. Now that the Field 

 Verification Program is complete and long-term monitoring has documented a chronic 

 response, the FVP mound should be capped in order to isolate the UDM from the 

 sediment/water interface and return the area to near-ambient conditions. In addition, the 

 movement of the disposal site boundaries to the west-southwest lends further support to 

 this recommendation. 



The low water column dissolved oxygen event that seemed to affect the FVP mound 

 was also noticed over the CLIS 94 and NHAV 93 mounds, as well as the three CLIS 

 reference areas (CLISREF, 4500E, and 2500W). Data obtained from the Connecticut 

 DEP indicated a summer hypoxia event occurred several days before the September 1995 

 monitoring cruise. The REMOTS® photographs obtained over the reference areas and 

 project mounds depict the aftermath of the low DO event within the benthic community. 

 The Stage I organisms occupying the surface sediments could represent benthic 

 recolonization as the DO concentrations began to rise approximately 10 days before the 

 survey. In order to avoid a downward trend or skew in future data, monitoring cruises in 

 the western and central Long Island Sound should be scheduled for early July. By 

 conducting environmental sampling activity earlier in the summer and avoiding the 

 possibility of recurring hypoxia, NED will gain a more realistic perspective of the benthic 

 community at the Long Island Sound disposal sites. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



