As previously noted, none of the sediment chemistry 

 results of the present study exceeded NERBC 'Moderate* upper 

 limits, except for Hg in the Norwalk Center sample, which fell 

 within the 'High' category of high contamination. Several of the 

 mounds were in the 'Low' range for all parameters tested. Those 

 that showed a predominance of 'Moderate' contaminant levels were 

 mounds which have received relatively contaminated dredged material 

 (FVP, CLIS-86, NH74, and, to a lesser extent, Norwalk). These 

 mounds were not capped and thus they do not show any "dilution" 

 effects in their sediment chemistry as a result of capping with 

 cleaner material. In comparison, the four capped mounds (CS-1, CS- 

 2, STNH-N, and STNH-S) had levels within the 'Low' category for all 

 parameters tested, suggesting that the caps have been effective in 

 isolating or possibly "diluting" contaminated dredged material with 

 cleaner sediment. 



For most of the mounds sampled, no statistically 

 significant differences were found for contaminent concentrations 

 between Top and Bottom core sections (Table 3-20) . However, MQR, 

 STNH-S and NH74 did show significantly greater concentrations in 

 the Bottom samples for some of the trace metals and percent total 

 carbon. In contrast, STNH-N Center showed a number of parameters 

 (Pb, As and Fe) to be significantly greater in the Top core section 

 sample. This was the only station that showed significantly less 

 % total carbon than the reference station in the Bottom sample 

 (Table 3-22) . In addition, this station also had the highest mean 

 RPD (4.64 cm) of all the disposal mounds sampled. In a natural 

 deposit ional system, trace metal distributions with depth are 

 controlled by the redox potential of the sediment, as well as the 

 supply of Fe and carbon (Benninger et al., 19XX) . Such variables 

 can help explain the observed results; however, the geochemical 

 system involved is complex and a study designed specifically with 

 these processes in mind would be required in order to assess their 

 role in controlling contaminent concentrations with depth at 

 specific disposal mounds. 



The sediment chemistry results for the transect of 

 stations sampled at STNH-N suggest that dredged material may have 

 reached some of the outlying stations as part of the original 

 disposal operation (Tables 3-10 through 3-18) . However, 

 statistical tests between the chemical results on these stations 

 and the Center showed no indication of systematic transport in a 

 specific direction (Table 3-23) . If transport of contaminanted 

 sediment from the Center to the outlying stations had occurred, a 

 decreasing concentration gradient at stations along the axis of 

 transport would be expected. This pattern was not observed in the 

 present results. 



It is important to recall that STNH-N is a capped mound 

 consisting of sand from New Haven Harbor overlying material from 

 Stamford, CT. Previous profiles of this mound showed the cap layer 

 with steep topography, ranging from a thickness of approximately 



39 



