74 



4A.2 REMOTS® Sediment-Profile Photography 



A total of 33 REMOTS® camera stations were occupied as part of the November 

 1996 field operations. The sediment-profile images collected in close proximity to the 

 pseudo-UDM deposit were used to characterize the Royal River material as dark silt 

 intermixed (mottled) with a light gray, stiff clay (representative of the glaciomarine 

 deposit; Figure 4-14A). Plant material and wood fragments were visible in several of the 

 replicate photographs obtained within the project area. Clumps of dredged material 

 detected on the surface of the seafloor, and chaotic sediment fabric at the sediment/water 

 interface, suggested that cohesive masses of sediments were released from the barges, 

 descended more than 60 m through the water column, and were deposited intact (Figure 4- 

 14B and C). 



The thickness of fresh dredged material was mapped using the REMOTS® camera 

 penetration data (Table 4-3). At many stations within 200 m of the center, the thickness of 

 pseudo-UDM exceeded camera penetration; penetration depths ranged from 9-17 cm 

 (Figure 4-15). The > 10 cm dredged material thickness contour incorporated all stations 

 within 100 m of the survey center, as well as at Stations 125ESE, 200ENE, and 200S 

 (Figures 4-15 and 4-16A). A few replicates at 50S, 50N, and lOOS indicated 3.5 to 8.8 

 cm of pseudo-UDM over ambient. Station 200SE had no penetration, consistent with the 

 baseline survey (Figure 4-7). 



Recently deposited Royal River material over ambient sediments, or historic 

 dredged material in the far northwestern stations, was detected at many of the peripheral 

 stations. A fine apron of material was measured at a few stations surrounding the main 

 pseudo-UDM footprint, with thin layers (<4 cm) of material measured at 200W, 300S, 

 and 300SE. With the exception of Stations 200N, 400SE, 400S, and 400NW, layers of 

 recently deposited dredged material with thicknesses > 1 cm covered the majority of the 

 survey grid (Figure 4-16B). 



The Royal River dredged material deposit was quickly recolonized by both small 

 and large benthic fauna, verifying the suitability of the project pseudo-UDM for 

 unconfined open water disposal (Figure 4-17). At one week postdisposal, RPD depths 

 ranging from 1 cm to 4 cm were detected in the majority of the sediment-profile images. 



4.4.3 Sediment Grab Sampling 



At nine of the REMOTS® stations, surface sediment grab samples were collected 

 over the pseudo-UDM deposit formed near the center of the Royal River Project Area. 

 The sediment recovered was sampled, preserved, and analyzed for grain size and the fine 

 fraction composition. 



TTie Portland Disposal Site Capping Demonstration Project, 1995-1997 



