67 



the presence of an apron of historical dredged material extending southeast from the 1990- 

 1991 position of the DG buoy (43° 34.1od''N, 70° 01. 900 'W) into the Royal River 

 Project Area, consistent with DAMOS disposal logs. The margin of the relic material was 

 sampled at Stations 400NW, 300NW, and 200NW. 



Ambient sediment, consisting of medium- to fine-grained tan sands commonly 

 intermixed with cobbles, was detected at many of the stations on the southern and 

 southeastern arms of the survey grid, as well as Stations 200N and 200NE (Figure 4-7). 

 Tan sand with traces of reduced silt (possible relic dredged material) was found at Stations 

 50NE. CTR, and 50SW. 



4.3.3 Planview Photographs 



The planview camera provides information on the character of the surface of the 

 seafloor. Photographs were collected within the northwest-southeast trending trough of the 

 survey area (Stations 400NW - 400SE; Figure 4-7). All but two stations had a smooth 

 silty seafloor in at least part of the camera's field of view. Heading southeast along this 

 transect, the photographs from 400NW and 300NW showed smooth fine-grained 

 sediments. Shrimp, shells, and a lobster pot trawl line were detected at 200NW. 

 Sediment-profile photographs indicated fresh dredged material at Station lOONW, 

 corresponding planview images displayed clam and mussel shell fragments partially buried 

 in the newly deposited silt (Figure 4-9A). Photographs collected over CTR displayed the 

 same types of shell fragments, as well as worm tubes, large burrowing anemones, and a 

 lobster (Figure 4-9B). 



Turbidity caused by the touchdown of the camera baseframe before the acquisition 

 of a planview image at 50NW prevented the collection of a clear image. The 

 corresponding sediment-profile image indicated the presence of a silt and sand at the 

 sediment/water interface. Scattered cobble to boulder size rocks appeared at Stations 50SE 

 and lOOSE (Figure 4-9C). A boulder sized rock at Station 300SE caused the REMOTS® 

 camera frame to lay on its side. The resulting planview photograph showed a very 

 irregular silt-covered rock outcrop. The last station in the transect planview photograph, 

 from 400SE, showed a smooth seafloor with scattered rocks. 



4.3.4 Side-Scan Sonar 



In conjunction with the February 1996 bathymetric survey operations, SAIC 

 collected side-scan sonar data over the southern region of PDS. Originally obtained to 

 assist in the placement of a bottom-mounted instrument array for physical oceanographic 

 studies (McDowell and Pace 1997), the acoustic images provided insight into the geology 

 and topographic features within the 1.95 km- area. The side-scan returns illustrated 



T}xe Portland Disposal Site Capping Demonstration Project, 1995-1997 



