^ 43_ 



3.4 Reference Areas 



Three reference areas for NLDS (NLON REF, NE REF, and WEST REF) were 

 surveyed with the REMOTS® sediment-profile camera. These reference areas provide a 

 basis for comparison in evaluating the overall health of the benthic community at NLDS. A 

 total of thirteen stations were surveyed. A complete set of image analysis results is provided 

 in Appendix B4. 



Surface sediments at the three reference areas were predominantly muddy (i.e., 

 silt/clay), with a grain size major mode of >4 phi (Table 3-2). There appeared to be a 

 significant component of very fine sand mixed with the silt/clay at almost all of the reference 

 area stations (i.e., "sandy mud"). One station at NLON REF contained predominantly very 

 fine sand (4 to 3 phi). In many of the images, sandy mud over mud stratigraphy was observed, 

 and organic detritus and/or shell Augments were present at the sediment surface. Similar to 

 observations at the disposal mounds, a depositional layer of organic detritus and both decaying 

 and intact amphipod tube mats were observed at the sediment surface at many stations. There 

 was no evidence of dredged material observed in any of the reference area images. 



The RPD depths at the reference area stations ranged ft-om 1 .96 to 3.58 cm, with an 

 overall average of 2.66 cm (Table 3-2). These values suggest good oxygen penetration into 

 the sediment, and there was no evidence of any low dissolved oxygen conditions. Stage II 

 was the dominant successional stage; active Stage III feeding voids were observed at only 

 five of the thirteen stations. Many juvenile amphipod mats were common at NE REF. 

 Decayed mats and juvenile amphipods were apparent at NLON REF and WEST REF. Two 

 images fi-om Station WR-5 in WEST REF also showed small clumps of mussels (likely 

 Modiolus sp.) inhabiting the surface sediments (Figure 3-20 A and B). 



The OSI median values ranged fi-om +5 to +9 (average of +7) and were very similar 

 to values observed in 1997 and 1998. Overall, the average OSI value of +7 suggests 

 relatively healthy or undisturbed benthic habitat quality at the three NLDS reference areas at 

 the time of the August 2000 survey. 



Monitoring Cruise at the New London Disposal Site, August 2000 



