EXECUTIVE SUMMARY 



The Western Long Island Sound Disposal Site (WLIS) contains four disposal 

 mounds formed since disposal began at the site in 1982. These mounds have 

 remained stable over time and with the exception of the area around the most 

 recent disposal point, have exhibited full benthic infaunal recolonization. Since the 

 last monitoring survey at WLIS (July 1988), approximately 185,000 m 3 of dredged 

 material has been released at the site. Locating this new dredged material, 

 determining the stability of mounds formed prior to July 1988, and assessing the 

 chemical and biological impact of disposal activity at the site were the objectives of 

 the July 1990 monitoring survey. 



As of August 1985 three disposal mounds existed at the site ("A, "B", and "C"). 

 Mound "C" continued to receive dredged material during the 1985/1986 disposal 

 season. From September 1986 to May 1988 dredged material was released at the "B" 

 mound. During the 1989/1990 disposal season the "D" mound was formed. This 

 disposal mound is 5.3 m high with a radius of 225 m. Comparison of the present 

 bathymetric survey with the last survey in July 1988 showed a stable height for 

 mounds "A" and "C" (decreases in height of 0.25 m) and a decrease of 1 m in height 

 for mound n B\ Since disposal was occurring at "B" just prior to the July 1988 

 bathymetric survey, the dredged material would have compacted between July 1988 

 and July 1990, possibly resulting in the 1 m decrease in height. Since the "A" and "C" 

 mounds have not received any new material since 1986, extensive compaction at 

 these locations is unlikely. 



The center of the "D" disposal mound exhibited rapid infaunal recolonization. 

 Stage III was the predominant successional stage, and Organism Sediment Index 

 (OSI) values were greater than +7. Many REMOTS® stations on the north and west 

 flanks of the "D" mound exhibit only Stage I organisms and OSI values less than +6. 

 The dark, low-reflectance of the sediments at these stations, combined with their low 

 consolidation, are typical of newly-deposited, organic-laden sediments with high 

 oxygen demand. This sediment is expected to reach Stage III recolonization and OSI 

 values > +7 over time given the rapid level of recolonization at the center of the "D" 

 mound. 



Near-bottom dissolved oxygen (DO) concentrations measured at the reference 

 areas and the "D" disposal mound ranged from 4.1 to 4.5 mgl" 1 . Although 

 significantly lower than corresponding near-surface values (9.2 - 11.8 mgl" 1 ), near- 

 bottom DO levels remained above hypoxic levels. 



