45 



• Capped mounds have remained in 

 stable configurations for up to 14 

 years. 



• Geotechnical modeling suggested 

 that consolidation occurs rapidly 

 upon completion of disposal. 



• The similarity of bathymetric 

 contours over the decade suggests 

 that erosion is minimal. 



• No evidence indicates that the cap 

 has been physically breached by 

 storms, strong bottom currents, or 

 any anthropogenic influence such as 

 bottom trawlers. 



• Qualitatively, the data favor 

 scheduling disposal operations 

 during the late winter-early spring 

 period to permit as much 

 consolidation and surface 

 stabilization as possible prior to the 

 onset of the fall hurricane season. 



3.2 Biological Characteristics 



From an environmental management 

 standpoint, the primary purpose of capping 

 is to isolate dredged material contaminants 

 from the biological communities found in 

 and around open- water disposal sites. 

 These contaminants have the potential to 

 affect local biota adversely and, through 

 food chain transfer, the larger environment 

 and potentially the human population. The 

 response of biological communities to 

 capped mounds should be considered of 

 primary importance in any evaluation of 

 capping programs. To date, there have 



been no clear indications of biological 

 disturbance from capped mounds after re- 

 establishment of a benthic community on 

 the freshly deposited material. One 

 possible exception to these conclusions 

 occurred at MQR and will be discussed 

 below. 



3.2.1 Early Monitoring Approaches 



Since the initiation of dredged material 

 disposal monitoring in Long Island Sound 

 in the early 1970s, all field surveys have 

 included components detailing selected 

 characteristics of the biological community 

 resident on and adjacent to the capped 

 disposal mounds. Initial surveys examined 

 both water column and benthic 

 components, with primary emphasis placed 

 on the benthic infaunal community 

 (Morton and Karp 1980). 



In benthic studies conducted from 1980 

 to 1983, grab samples of the surface 

 sediments were obtained with a 0.1 m 2 

 Smith-Mclntyre sampler and sieved 

 through 1.0 mm sieves. Macrofauna were 

 sorted, identified, and counted to obtain 

 measures of community structure (Brooks 

 1983). Most of the variability observed 

 within the benthic data appeared to be 

 related to the combination of disturbance 

 (Rhoads et al. 1978) and variations in 

 sediment grain size (Brooks 1983). 

 Temporal and/or spatial variations in 

 population characteristics could not be 

 associated simply with sediment chemistry. 

 Trace element and volatile solids 

 concentrations measured at the center of 

 STNH-N and STNH-S were approximately 

 equal to or less than those measured at the 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



