90 



lack of clear evidence of recent Stage III activity. There were no indications of low DO 

 conditions within the surface sediments, and no methane detected. 



3.1.3 August 1992 Dissolved Oxygen Measurements 



Near-bottom (approximately 1 m above the bottom) dissolved oxygen concentrations 

 sampled on 7 August 1992 at the disposal site and the three reference areas ranged from 

 7.3 mg/L to 7.8 mg/L. Dissolved oxygen concentrations in the top two meters of the 

 water column were slightly higher than those measured in near-bottom waters, ranging 

 from 7.7 mg/L to 8.1 mg/L. The concentrations of dissolved oxygen were uniformly 

 distributed throughout the disposal site and reference areas. These concentrations are not 

 limiting to benthic organisms (Tyson and Pearson 1991). 



3.2 USCGA Disposal Mound 



3.2.1 Bathymetry 



The USCGA dredged material disposal mound was formed when 124,000 m 3 of 

 dredged material from the Eagle Pier project at the U.S. Coast Guard Academy was 

 released at NLDS between the historic NL-TR and NL-RELIC disposal mounds. A 

 1600 m x 1600 m precision bathymetric survey was conducted in August 1995 to 

 document changes in seafloor topography relative to the survey performed in August 1992 

 (Figures 3-34 and 3-35). 



A 0.86 km 2 area surrounding the USCGA buoy was selected as an area of detailed 

 analysis to facilitate accurate depth difference calculations. The material dredged from the 

 US Coast Guard Academy was sequentially deposited, forming an irregularly shaped 

 sediment mound 420 m wide and 1 m high at the apex (Figure 3-36). There was a 0.5 m 

 high ridge of sediment that extended approximately 320 m southwest from the center of the 

 mound. Another lobe of sediment extended 350 m from the mound center to the north- 

 northeast and was 190 m wide. 



3.2.2 REMOTS® Sediment-Profile Photography 



A 13-station REMOTS® sediment-profile photography survey was completed over 

 the USCGA mound in August 1995 to document the benthic recolonization status. A 

 complete set of REMOTS® image analysis results for the August 1995 survey of the 

 USCGA mound is presented in Appendix B. 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



