59 



calculated OSI values. The successional sere of each station was also entirely unchanged 

 relative to 1991, with Stage III organisms present at three of the five stations. 



In addition to the measured REMOTS® parameters, a qualitative assessment of the 

 photographs between the two surveys showed a lightening of the sediment fabric in 1992. 

 The very dark subsurface sediments noted in 1991 were not nearly as prominent in 1992 

 (Figure 4-1). This was interpreted to indicate that the upper sediment layers had experienced 

 some oxygenation and reworking during the period between the 1991 and 1992 seasons. On 

 the whole, REMOTS® photographs indicated only a modest improvement in habitat quality at 

 the stations of concern. 



The amphipod bioassay showed no significant toxicity in sediment samples taken 

 from either WLIS "D" or "A" relative to reference area 2000W. One of the five WLIS 

 "D" replicate samples had greatly reduced survivorship (25%) relative to the other four 

 replicates. Since each WLIS "D" replicate was a composite of four stations, this low value 

 could not be associated with any single station. This apparent outlier was also not explained 

 by observed conditions during the testing period, but it was not different enough to 

 significantly influence the mean WLIS "D" survivorship. Overall, the toxicity testing 

 clearly demonstrated a lack of difference between the stations of concern, and the reference 

 areas. 



Within the framework of the tiered monitoring plan a failure to demonstrate 

 significant toxicity in the sediment bioassay tests generates a preliminary assumption that 

 physical or biological processes caused the unusual sediment conditions. Under these 

 circumstances, no immediate remedial action is required. However, the stations are 

 recommended to be reassessed within 12 months for further changes in the benthic 

 community. In addition, the tiered monitoring plan suggests that any extraneous conditions 

 that might affect benthic colonization also be evaluated. In the western Long Island Sound 

 area intermittent periods of low dissolved oxygen are a potentially important source of 

 disturbance to the benthos. However, low oxygen conditions were not observed during the 

 present survey, and adjacent mounds and reference areas exhibited no signs of response to 

 seasonal anoxia. 



4.3 Selection of Alternate Reference Areas 



Two new potential reference areas (SOUTH and EAST) were evaluated to replace the 

 existing 2000S and WLIS-REF areas. This evaluation consisted of chemical and physical 

 analyses of grab samples, REMOTS® data, and rough bathymetric checks of the possible 

 new areas. The results show that SOUTH is a suitable replacement for 2000S. 

 Unfortunately, it was not possible to locate an area north of the disposal site that did not 

 exhibit some evidence of historic dredged material. As a result, both the EAST and WLIS- 

 REF areas were roughly equivalent, and therefore not suitable as reference areas for ambient 

 bottom. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1992 



