137 



The greatest total PAH concentration, 1060 u.g/kg, occurred in the Outer Zone in the 

 1-1.7 m sample of Core 17A, indicating an elevation in the ambient eastern Long Island 

 Sound sediments (possibly related to historic dredged material disposal) occurring below a 

 CDM layer of at least 1.0 m. The Middle Zone long Core 19 A, located on the edge of the 

 UDM deposit, may have contained small amounts of UDM in the 0.5-1.0 m section as 

 indicated by the slightly higher normalized PAH levels than present at the reference station 

 (Figure 4-14). Although the long core from the Inner Zone (Core 23A) had visually apparent 

 UDM, the normalized PAH concentrations were consistent with other measured values 

 (Figure 4-14). In long Core 23A, the section below 1 10 cm was described as black, oily fine 

 sand, and both samples below 75 cm had high TOC concentrations (>5.5%). The 1-2 m 

 depth interval contained 20% gravel content, 37% sand, and only a 43% silt and clay fraction. 

 Core 23A was the longest (3 m) and yet did not appear to contain ambient sediments. The 

 PAH concentrations were rather low in the 0.5-0.75 m interval of Core 23A and increased 

 with depth. The cumulative evidence of increasing PAH concentrations, high TOC, and an 

 atypical grain size distribution suggested that long Core 23A did penetrate into UDM. 



To summarize the chemistry and physical characteristics of the cores taken from the 

 Seawolf Mound, in all samples between the surface and 50 cm depth intervals in the cores, 

 metal and PAH concentrations were comparable to CDM material and in two cases 

 marginally higher than Reference area values for metals normalized to grain size (Cores 3A 

 and 14B). The long cores did not sample any material with strongly elevated chemistry 

 values, but changes in grain size, TOC, appearance and chemistry indicated two cores that 

 may have sampled UDM (Cores 19A and 23 A) and a third core (Core 17 A) may have been 

 influenced by historic contamination in the existing, pre-Seawolf sediments. In each of these 

 cores, the elevated chemical concentrations were found at depths below 50 cm. 



The data from 1997 and 1998 were very consistent and indicate that the sediments on 

 the surface of the Seawolf Mound were not elevated in contaminants relative to the original, 

 pre-dredged testing of the channel sediments. Where higher concentrations were found at 

 depth in the cores (all 50 cm or deeper), there was no evidence of elevation in the top core 

 intervals relative to other samples. The weight of the chemical evidence combined with 

 biological and REMOTS® sediment profile images indicates that the cap was effective in 

 isolating the underlying UDM deposits, with no evidence of mixing or release of contaminants 

 into the surface sediments. Furthermore, the chemistry data clearly showed a minimum of 

 50 cm of suitable material covering the mound at all sites cored. In the case of the long cores, 

 the capping material was shown to be much thicker (1.6 to 2.0 m thick in 1997, 0.5-2.0 m 

 thick in 1998). The results of the core analyses support a conclusion that the Seawolf Mound 

 was capped with at least 50 cm of material, and this cap material was effective in 

 consolidating and isolating the underlying UDM material. 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



