12 



obtained from the REMOTS® photographs will be applied to the site in general based on the 

 assumed presence of relic dredged material throughout the site (see above). The results of 

 the REMOTS® image analysis are presented in the Appendix. 



3.2.1 Sediment Features 



Grain size ranges are estimated visually by comparing the sediment image to the 

 Udden-Wentworth size classes. The Udden-Wentworth size class system is a standard grain 

 size measurement ranging from greater than 4 phi (silt/clay) to less than -1 phi (gravel). A 

 major mode (the most common grain size) and the range of grain sizes are estimated. 



The Bridgeport Disposal Site is dominated by sediments with a major mode of 1 to 

 >4 phi, i.e., medium sand or finer. Thin surface layers of coarse sand were also observed 

 among three stations: B27, B30, and B32. 



Some stations exhibiting relatively high modal grain sizes (1 or less) also contained 

 shell fragments and mudclasts. Shell fragments were present in 25 percent of the Bridgeport 

 photographs, and mudclasts were present in 50 percent of .he REMOTS® photographs 

 (Figure 3-3). Mud clasts are typically associated with the reduction of topographic relief due 

 to physical and biological processes. While fine-grained sediment is reworked into ball 

 structures and concentrated in topographic lows, coarse-grained materials, including shell 

 fragments, are concentrated at the crest of the gradually decaying mound (SAIC 1984). 

 Localized disturbances, such as trawling activities, may also disturb relic dredged material 

 and initiate the formation of small mud clasts. Evidence of trawling was noted on the side- 

 scan records (Figure 3-4). 



Both oxidized and reduced mudclasts were observed at the Bridgeport Disposal Site. 

 While the presence of reduced mud clasts in an aerobic setting is sometimes indicative of 

 recent origin (Germano 1983), the mud clasts in this survey were well rounded, suggesting 

 the clasts were not recently formed. The clasts may have been generated from underlying 

 reduced sediments that were brought to the surface by relatively recent disturbances. 

 Disturbances could have been physically or biogenically induced. 



3.2.2 Surface Boundary Roughness 



Boundary roughness is the vertical distance between the highest and lowest points of 

 the sediment-water interface. Boundary roughness values at Bridgeport ranged from 0.17 to 

 5.46 cm with a mean boundary roughness value of 1.4 cm. The surface relief is both 

 physically induced, reflecting either bottom disturbance (scour depressions, mud clasts) or 

 natural bedforms (sand ripples), and biogenically created, including infaunal burrows or 

 mounds. Physical processes accounted for most of the relief at the historical Bridgeport 

 Disposal Site. 



Reconnaissance Survey of the Historical Bridgeport Disposal Site, August 1992 



