102 



zone Core 17A and inner zone Core 23 A; the values marginally exceeded the WEST REF 

 values for some compounds below 0.75 m in these two zones. In contrast, in the middle 

 zone (Core 19A) the highest total PAH levels occurred within the top (0.5 to 0.75-m) depth 

 interval and decreased with depth. 



The 1998 short and long core data were compared with the 1997 results. All of the 

 tested analytes were the same, except for dibenzofuran, which was not tested in 1998 and 

 was below detection levels in 1997. The 1998 reference area core contained over double the 

 concentration of total PAHs (457 (ig/kg) compared to those detected in 1997 (166 u.g/kg). 

 For the short cores taken at the Seawolf Mound, the mean value of total PAHs in 1998 

 (387.2 |ig/kg) was higher than observed in 1997 (166 |J.g/kg). The range of values for the 

 total PAHs in the short cores was narrower in 1998 (100-646 |J.g/kg) than in 1997 (107- 

 733 (ig/kg). The 1998 long cores were taken from the same stations used in 1997, however, 

 the results were more variable. The 1998 long core data also indicated higher concentrations 

 of PAHs than observed in 1997. Trends and comparisons are described in more detail in the 

 Discussion (Section 4.0). 



3.2 NLDS Reference Areas 



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

 surveyed with the REMOTS® sediment-profile camera in September 1997 and July 1998. 

 These reference areas provide a basis for comparison with the images collected over the 

 NLDS project mounds and aid in determining the health of the benthic community within the 

 disposal site. The conditions at NLON REF, NE REF, and WEST REF are presumed to 

 reflect seasonal and annual variations in environmental conditions. In each year a total of 13 

 randomly selected stations were surveyed with the REMOTS® sediment-profile camera at 

 NLON REF, NE REF and WEST REF reference areas. Four stations were surveyed in NLON 

 REF, four at WEST REF, and five in the NE REF. Three replicate photographs were collected 

 at each reference area station and subjected to the identical series of measurements and criteria 

 used to characterize benthic habitat conditions within the disposal site. These data were used 

 as the basis for comparison in assessing benthic habitat quality over the Seawolf Mound. A 

 complete set of REMOTS® image analysis results for each reference area and each survey are 

 presented in Appendix B. 



3.2.1 September 1997 Survey 



No dredged material was present in any of the replicate photographs obtained from the 

 three reference areas. Replicate averaged camera penetration depth ranged from 4.6 cm to 

 10.3 (Table 3-2). The shallow to moderate camera penetration reflected limited sand-over- 

 mud layering at several stations within each reference area. All of the reference areas showed 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



