120 



REMOTS® and core data were used to evaluate the overall footprint of the mound, rather 

 than using these tools only to confirm the presence of the outlying apron. 



The thickness of the pseudo-UDM deposit was mapped using REMOTS® 

 information from the pseudo-UDM survey in November 1996, and the thicknesses of 

 pseudo-UDM collected by the cores during the postcap survey. At many stations the 

 REMOTS® data provided only a minimum thickness, as often the dredged material was 

 thicker than the penetration of the REMOTS® camera. The core thicknesses should also be 

 considered minimum, because the measurements were made after the placement of the cap 

 so the material probably consolidated to some extent. In addition, only two cores acmally 

 penetrated into ambient, so that the pseudo-UDM collected in the postcap cores was 

 estimated as minimum thickness (as displayed on Figure 5-1). 



The maximum thickness of pseudo-UDM ( > 20 cm) as measured by REMOTS® and 

 cores was concentrated to the southeast of the buoy, consistent with bathymetric data. The 

 core data (Core G2) indicated that the bathymetric footprint was indeed overestimated in 

 the eastern lobe, as a 22 cm layer of pseudo-UDM was measured over ambient, rather than 

 the 75 to 100 cm calculated by the depth difference method (Figure 5-1). 



Within 100 meters of the disposal point, sediment-profile images and core data 

 resulted in pseudo-UDM thicknesses of 10-20 cm, often greater than camera penetration 

 (maximum value > 17 cm). The spread of dredged material was limited to within 200 m 

 (upslope) towards the NW, but was present west, east, and south of the disposal point 

 (Figure 5-1). The only exception was the station located 200 m SE of the center, which 

 was located on a rocky, high point as determined from the baseline REMOTS® survey. 

 There was an apron of material of approximately 3 cm towards the south and east located 

 at those stations measured 300 m away from the center, including 300S and 300SE 

 (downslope). No pseudo-UDM was measured at the stations located 400 meters away 

 from the center. 



These data suggested that the overall spread of material was relatively consistent 

 with the DAMOS Capping Model. The model predicted a circular deposit around the 

 center disposal point with a radius of 250 m (diameter 500 m). Because of the slope of the 

 basin towards the southeast, the material predictably spread further in that direction 

 (between 300 and 400 m) relative to the northwest ( <200 m), so that the north-south axis 

 of the deposit, according to the REMOTS® data, was approximately 500 m (Figure 5-1). 

 In general, the deposit of pseudo-UDM appeared to be slightly smaller than predicted by 

 the model, but because of the slope and the overall uneven bottom topography, the actual 

 footprint was probably patchy and therefore difficult to reliably contour, especially with 

 many values representing minimum thicknesses. 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



