38 



calculated volume of Stamford material at 

 STNH-S to within approximately 95% of 

 the barge estimate (Morton 1980a). 



Comparisons showed material losses of 

 both cap and mound at the southern site 

 ranging from 3 to 5 % , with the majority 

 of in-place material residing in the well- 

 defined capped deposit (Morton 1983b). 

 Given the resolution of the acoustic system 

 and the errors inherent in disposal barge 

 volume estimates (Tavolaro 1984), the 

 overall agreement between the bathymetric 

 data and the disposal barge logs must be 

 considered excellent. The indicated losses 

 are similar to those previously reported 

 (Gordon 1974, Bohlen 1978) and suggest 

 limited far-field dispersion of sediments 

 and associated contaminants during 

 disposal. 



Volume calculations based on depth 

 differences of New Haven material at 

 STNH resulted in subsequent placement of 

 33,000 m 3 of sand over STNH-N and 

 72,000 m 3 of silt over STNH-S. 

 Comparisons at the northern site were 

 complicated by the high water content of 

 the sands induced by the hydraulic dredge. 

 The bathymetric surveys showed minimal 

 lateral spreading of the initial capped 

 deposits (Figure 3-2). The major changes 

 in dimensions induced by capping were 

 confined to the vertical. Both deposits 

 were well-covered with cap material: cap 

 thicknesses ranging from approximately 

 3.5 m on STNH-N to more than 4.5 m 

 over STNH-S after capping operations in 

 spring-summer 1979 (Figure 3-2 and 3-3; 

 Morton 1983b). 



The STNH project also showed that 

 coarser grained material could be placed 

 over finer grained deposits without 

 significant displacement and/or dispersion 

 of the finer material. Comparisons of pre- 

 and postcapping bathymetric contours 

 indicated that major changes were confined 

 to the buoy locations. Spreading of the 

 flanks was more pronounced at STNH-N, 

 but diver observations showed this to be 

 primarily the result of sand movement 

 rather than dispersed silt-clays (Figure 3-2; 

 Morton and Karp 1980, Morton 1983b). 

 The upper surface of the central part of 

 STNH-N consisted primarily of New 

 Haven material, and vertical overturning 

 or mixing during cap placement appeared 

 to be minimal from diver observations. 

 This was later confirmed by visual and 

 chemical analyses of coring investigations 

 (Section 4.0). 



The later addition of New Haven 

 capping material (-110,000 m 3 ) in the 

 spring of 1980 (Table 2-4) was followed 

 by a bathymetric survey in June 1980. 

 Much of this material was disposed at the 

 center of STNH-S to cover a small, 

 secondary volume (6,000 m 3 ) of Stamford 

 material deposited on the 72,000 m 3 cap. 

 However, 34 barge loads were disposed at 

 specific LORAN-C points to thicken the 

 cap south and west of the buoy (SAI 

 1980b). Comparison of the June 1980 

 bathymetric survey to the prior survey in 

 November does not reveal a large increase 

 in the overall height of STNH-S. 

 However, the June profile does reflect a 

 wider distribution of material, especially to 

 the west where a new pile was detected 

 (Figure 3-4). 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



