66 



Mill River sediments, which are relatively 

 high in many metals (especially Hg and 

 Cd), have a very low oil and grease 

 component. There is little difference in 

 arsenic concentrations between mound and 

 cap sediments from these areas. Based on 

 metal analyses, sediments from Quinnipiac 

 River, as already discussed, were 

 originally intended as capping material for 

 Mill River sediments, but actually contain 

 a high enough percentage of volatile solids 

 to be considered highly contaminated. 

 Finally, except for Hg, the contaminant 

 concentrations of Norwalk cap and mound 

 sediments are within the ranges of most of 

 the other cap sediments. Therefore, any 

 discussion of the contaminant 

 concentrations in dredged sediments must 

 be considered relative, and does not 

 specifically address how detrimental a 

 particular sediment is to the biota, or what 

 the synergistic effects of different 

 contaminants may be. 



Theoretically, any capped mound will 

 consist of three components, or end 

 members: moderately to highly 

 contaminated mound material, relatively 

 uncontaminated capping material, and 

 background, or ambient, material. Any 

 sediment sampled, during either the 

 formation or monitoring phase, will 

 contain one or more of these three 

 components. If each one has a distinct 

 chemical signature, any random sample 

 can be distinguished as being mound, cap, 

 or background material, or a composite of 

 two or more components. 



There are six source areas of dredged 

 sediments for the NED projects discussed 



in this report. Sources of mound material 

 (more contaminated sediments) include 

 Stamford Harbor (ST), Norwalk Harbor 

 (highly contaminated), Mill River, and 

 Black Rock Harbor (BR). Capped 

 sediments were commonly derived from 

 New Haven Harbor (NH). Quinnipiac 

 River sediments were used for the first cap 

 at MQR, and low to moderately 

 contaminated sediments from Norwalk 

 Harbor were used for capping material at 

 NOR. 



Surface sediments sampled in the 

 source harbors appeared to have relatively 

 uniform sediment textures but highly 

 variable contaminant levels (Tables 2-1 

 and 2-3). Despite the widely varying 

 ranges of contaminant levels in both 

 mound and capping material, several 

 distinct characteristics permit more 

 detailed analysis of the sediment grab 

 samples. For example, New Haven sand, 

 which constitutes the cap at both STNH-N 

 and CS-2 and is represented by sample 

 FD-7 from New Haven Harbor, contains 

 concentrations of metal and organic 

 contaminants that are markedly lower than 

 either background levels of concentrations 

 in other New Haven materials (Figure 3- 

 15). The chemical and physical properties 

 of the sand cap make this material clearly 

 distinguishable from the mound material as 

 seen in sediment cores (Section 4.0). 

 Surface sediments at both MQR and CS-1 

 have the highest ranges of contaminants 

 measured in capping material, as 

 represented by sample FD-5 taken in New 

 Haven Harbor (Figure 3-15). 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



