83 



some of the PAHs, pesticides, and TRPHs 

 (40N from 40 to 60 cm) that was well 

 within the cap sediments (Figure 4-2), 

 although these compounds were low or 

 below detection levels in the interval 

 between 40 and 60 cm and the top of the 

 mound material. This suggested either 

 that there had been lateral movement of 

 organic contaminants without 

 accompanying movement of metals or, 

 more likely, that the New Haven dredged 

 material had patches of relatively 

 contaminated sediments. 



Three of the five cores taken at CS-2 

 (80N, 50W, and 40E) did not penetrate 

 mound material and had correspondingly 

 low chemical contaminant concentrations. 

 As at STNH-N, these low concentrations 

 were indicative of the sand material used 

 as a cap at both CS-2 and STNH-N. A 

 relatively high R 2 value of 0.800 occurred 

 at the 60-cm interval of 80N. This was 

 coincident with the boundary between base 

 and cap (Figure 4-3) and was due to the 

 base material having higher values of 

 vanadium (V) and Zn and a peak of 

 TRPHs in the 40-60 cm interval. The 

 hydrocarbon peak in apparent cap material 

 again testified to the chemical variability 

 of dredged material. The results at 80N 

 indicated that cap material was deposited 

 where there was no mound material, with 

 little or no mixing of cap and base 

 sediments. 



The highest R 2 value at CS-2 occurred 

 at 80NE, but not where the boundary was 

 visually located. The statistical (chemical) 

 boundary occurred at 60 cm (0.965) 

 whereas the visual boundary occurred at 



approximately 80 cm. This difference 

 may be an artifact of sampling because the 

 visual dredged material interval occurred 

 in a narrow band (20 cm) between cap and 

 base. However, there is a possibility of 

 mixing of, or migration from, that 20-cm 

 interval. 



The CTR station at CS-2 was the most 

 problematic. PC A analyses showed no 

 boundary with an R 2 greater than 0.7, even 

 though there was a visual distinction 

 between shell hash and black mud 

 described as mound material (Figure 4-3). 

 The contaminant values at the CTR station 

 fell between the ranges measured for 

 normal CS-2 cap material and for sediment 

 from Black Rock Harbor where the mound 

 material was obtained (Figure 4-6). These 

 intermediate values extended throughout 

 most of the core (20-120 cm), although no 

 distinctive Black Rock material was 

 recovered at CTR. 



The intermediate contaminant values of 

 samples recovered at CS-2 CTR could 

 represent a remnant of mixing of cap and 

 mound, evidence of contaminant 

 mobilization, or an isolated pile of more 

 contaminated New Haven sediment. 

 Mixing was unlikely since this core was 

 taken at the center of the capped mound 

 where the cap presumably is thickest, and 

 no evidence of mound material was found 

 at three of the other five core locations. If 

 the intermediate contaminant values were a 

 result of chemical migration from mound 

 to cap, an additional explanation for the 

 isolated occurrence at the CTR station 

 (i.e., no similar intermediate values were 

 measured at CS-2 80NE) is required. The 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



