EXECUTIVE SUMMARY 



Material dredged from the Thames Shipyard and Repair Company was released in the 

 northeast quadrant of the New London Disposal Site in October 1988, forming the NL-TR 

 disposal mound. The 13,303 m 3 of dredged material was classified as unsuitable for 

 unconfined open water disposal and was capped with 59,500 m 3 of clean material between 23 

 October 1988 and 23 January 1989. After a survey of the capped site in February 1989 it 

 was recommended that additional cap material be released at the site. From 13 March to 17 

 June 1990, 39,483 m 3 of supplemental material was deposited. 



In addition to the 1989 and 1990 capping operations, approximately 21,200 m 3 of 

 dredged material from Noank and Mystic, CT was released at Buoy 88 (41° 16. 100' N, 

 72°04.350' W), a separate disposal point approximately 700 m south of the NL-TR disposal 

 mound. The objectives of the most recent monitoring cruise at the New London Disposal 

 Site were 1) to delineate the extent and topography of dredged material deposited since the 

 August 1988 survey, 2) to determine mound stability, and 3) to assess near-bottom dissolved 

 oxygen concentrations relative to REMOTS® benthic analyses. 



Sampling was concentrated at two regions of recent disposal activity. The first 

 location, designated NL-TR, was a region where sediments unsuitable for unconfined open 

 water disposal were covered with a cap of clean material during early 1989. The second 

 disposal location, identified as NL-88, was immediately adjacent (150 m west) to the former 

 active mound listed as NL-85 in the July- August 1988 survey (SAIC 1990d). 



The bafhymetric survey revealed that 46,700 m 3 of new sediment had accumulated in 

 the vicinity of the NL-TR capped mound since the July- August 1988 survey. The radius of 

 dredged sediment deposited at NL-TR was approximately 550 m x 400 m, and benthic 

 recolonization was largely as anticipated, indicating a healthy recovery well within expected 

 recolonization rates. A comparison of precapping and postcap bathymetry indicated less than 

 50 cm of cap material on three of the six disposal points designated for the 1988 capping 

 operation. However, it is believed that consolidation of the underlying dredged material may 

 have contributed to the apparent diminished cap thickness. As a precaution, future disposal 

 operations should be directed to these three capping points. 



The bathymetric survey also indicated an accumulation of an additional 11,560 m 3 of 

 material in the southern portion of the disposal site at disposal mounds NL-85 and NL-88. 

 The REMOTS® survey at NL-85 found that dredged material was distributed across the 

 mound and that benthic recolonization was substantially as predicted (Stage II and III). 



Water column profiles of temperature, salinity, and density (sigma-t) showed that 

 little stratification of the water column existed during the period of the survey. Near-bottom 

 dissolved oxygen concentrations were uniformly high at all stations, both on and off the 

 disposal site, and there was no indication that dredged material disposal operations were 

 adversely influencing oxygen concentrations in the region. 



