4.4 Sediment Chemistry and Grain Size 



Results of the sediment grain size analysis demonstrate 

 a major mode of fine sand (4-2 phi) throughout most of the area. 

 Reference area 3 contained a Class II (NERBC) level of fines (>4 

 phi) . The distribution of material corresponded with results 

 obtained in the REMOTS® survey and supported the interpretation of 

 an apparent transport of fine-grained materials to the southeast. 



Sediment chemistry results indicated low levels of 

 metals, pesticides, PCBs, and PAHs. Distribution of these 

 materials was highest on stations containing greater amounts of 

 clay and organic matter (% TOC) and lowest on those containing more 

 than 90% sands (stations 1 and 20) . The affinity for these 

 pollutants to the colloidal material in sediment is well documented 

 (Pequegnat et al . , 1990) . 



The levels of PAHs found were low in comparison with 

 levels detected near the Fox Point area of Narragansett Bay (Pruell 

 et al. . 1985). Near the Fox Point area, levels of total PAHs were 

 found in the 2-3 ppm range while, in contrast, New Bedford Harbor 

 contained high-molecular PAH concentrations that were at least 2-3 

 times higher than those at Fox Point (Pruell et a_l. , 1990) . 

 Narragansett Bay is considered to be a relatively unpolluted urban 

 estuary while New Bedford Harbor is a highly contaminated estuary 

 (Pruell et al. , 1985, 1990). 



5.0 CONCLUSIONS 



The information obtained from the bathymetric survey and 

 REMOTS® photos permitted the detection of two disposal mounds 

 within the surveyed area. The primary mound was central to the 

 disposal site, 1.2 m high and 60 m wide. The other, south and west 

 of the center mound, was 1.6 m high and approximately 90 m wide. 

 Currents are most likely the dominant force contributing to a 

 bedload transport of fine-grained material from the northwest to 

 the southeast. 



The sediment grain size analysis was in agreement with 

 results obtained in the REMOTS® survey, and both sets of results 

 corresponded with the major mode distribution found in the 1981 

 survey. Sediment chemistry results indicated low levels of 

 pollutants. 



Although species richness was somewhat higher at the 

 reference stations, both on-site and off-site stations were well 

 within the range observed in soft-bottom, shallow-water 

 environments. Significant differences existed between reference 

 stations and on-site stations in REMOTS® parameters for RPD depth, 

 successional stages, and OSI values. Currently, the surveyed area 

 is healthy biologically and relatively uncontaminated. Based on 



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