

3.0 RESULTS 



3.1 Side-scan Sonar 



The historical Bridgeport Disposal Site, based on the results of the side-scan survey, is 

 mottled with relic, low-relief dredged material deposits. The natural or ambient bottom in 

 the western portion of the site exhibits a predominantly smooth, low-reflectance, silty texture 

 (Figure 3-1). Numerous low-relief, high-reflectance features, inferred to be dredged 

 material, are present throughout the disposal area but are concentrated in the central portion 

 of the site (Figure 3-2). The mottled, patchy appearance of these strong acoustic reflectors, 

 or targets, is characteristic of dredged material deposits and is due to alternating patches of 

 high- and low-reflectance materials. Strong reflectance of dredged material deposits relative 

 to the ambient, smooth bottom is a function of increased acoustic backscattering at the surface 

 of the deposit. This backscattering is likely related to increased microtopography and surface 

 roughness (i.e., coarse-grained texture) of dredged material in comparison to smooth, 

 ambient sediments. While storm activity may reduce the topographic relief of dredged 

 material mounds, net deposition in Long Island Sound is slow, approximately 1 mn7yr. 

 Coarse-grained dredged t..attrial covered by a thin surface deposit may be soiic-n/ letected 

 with side-scan sonar whi v has a small degree of bottom penetration. ' 



The mottled texf ire has been observed in other side-scan sonar surveys of 'lodged 

 material disposal sites on the West Coast and is caused by one or more of the followuig 

 processes or events (SAIC 1990c, 1990d): 



• physical and/or biological reworking of the deposit, producing a smooth, low- 

 reflectance signature; 



• disposal of sandy material with some cohesive silts; 



• random spacing of individual disposal operations of cohesive silty material; or 



• transport and deposition of sediments over the dredged material. 



Recently deposited dredged material will typically form a localized, circular high-reflectance 

 pattern in side-scan sonar traces (SAIC 1987, 1990c). The mottled appearance and low relief 

 of dredged material in this survey suggest that the acoustic reflectivity of the material has 

 decayed due to physical or biological reworking of the deposit or that natural deposition over 

 the last fifteen years has covered portions of the relic dredged material. 



3.2 REMOTS® Sediment-Profile Photography 



The physical and biological parameters discussed in this section pertain to those areas 

 sampled using REMOTS® sediment- vertical profiling. These areas are restricted to the 

 northeastern and southwestern quadrants of the site. For purposes of discussion, the data 



Reconnaissance Survey of the Historical Bridgeport Disposal Site, August 1992 



