52 



Fox Point, RI, New Bedford Harbor, MA, and DM28 of the New York Mud Dump 

 Site offer a high end comparison with elevated levels of LMW and HMW PAHs, especially 

 the LMW PAHs phenanthrene and anthracene, and the HMW PAHs fluoranthene, pyrene, 

 and benzo(a)anthracene. DM11 of the New York Mud Dump Site represents the mid-range 

 with concentrations of many PAHs below the 300 ppb detection limit, except for elevations 

 in the HMW PAHs fluoranthene, pyrene, benzo(a)anthracene, and benzo(b)fluoranthene. 

 Values for LMW PAH compounds at the NLON reference areas were similar to those 

 detected in the relatively unpolluted section of Narragansett Bay at North Jamestown with the 

 exception of higher levels of phenanthrene at NLON. HMW PAH levels were between those 

 values measured in North Jamestown, Rhode Island and Fall River, Massachusetts. 



4.4 Bottom Water Dissolved Oxygen 



The objective of the DO sampling was to assess near-bottom DO concentrations at the 

 reference areas and active disposal site in relation to benthic habitat conditions at the site. 

 Bottom waters will generally remain well oxygenated in the absence of a strong pycnocline. 

 Oxygen concentrations measured at approximately 1 m above the bottom at the disposal site 

 and reference stations ranged from 7.1 to 7.7 mg-1' 1 . The lack of low-oxygen bottom water 

 was consistent with the presence of oxidized surface layers of sediment (as determined by the 

 RPD) at the disposal site and reference stations. Surface oxygen concentrations ranged from 

 7.1 to 7.6 mg-1" 1 . These results indicated uniformly high oxygen concentrations across the 

 region and confirmed the prediction that oxygen levels would be similar both on and off the 

 disposal site. The similarity in near-surface and near-bottom oxygen values indicates a well- 

 mixed water column and no problem with hypoxia. The measured DO values were 

 consistent with near-surface oxygen values (at the time of the June survey) of 7.6 to 

 8.6 nig-l -1 (recorded with YSI oxygen meter) in the vicinity of NL-TR during July 1990 

 (Table 4-4). Near-bottom oxygen values for the 1990 survey as measured by modified 

 Winkler titration were 8.3 mg-1. 



Table 4-4 



Dissolved Oxygen Concentrations (mgT 1 ) at the 

 New London Reference Stations, July 1990 



Station 



Depth 



Surface 1 



Bottom 2 



NLON-REF 



18 m 



7.6 



8.3 



NE-REF 



15 m 



8.6 



8.3 



WREF 



23 m 



8.4 



8.3 



1 = Measured with YSI oxygen meter 



2 = Measured by Winkler titration 



Monitoring Cruise at the New London Disposal Site, June 1991 



