I3J_ 



6.0 CONCLUSIONS 



• A discrete, capped dredged material mound was created and detected on the 

 seafloor of Portland Disposal Site in the Royal River Project Area. Analysis of 

 REMOTS® sediment-profile images, cores, and envirorraiental tracers detected a 

 discernible difference between the CDM, pseudo-UDM, and ambient material. 



• An accumulation of pseudo-UDM was detected to the south and southeast of the 

 PDA buoy position using single-beam bathymetry and REMOTS® sediment- 

 profile images, most reliably in the relatively flat-bottomed basin targeted for 

 disposal. 



• Accurately detecting material in the surrounding area of more complex 

 topography by single-beam bathymetry alone was complicated by survey 

 artifacts. A more accurate measurement of the thickness and footprint of the 

 disposal mound could be obtained using higher resolution acoustic methods (i.e., 

 multibeam). 



• The relatively small volume of CDM placed over the initial pseudo-UDM 

 deposit was measured and mapped with the use of sediment-profile photography 

 and cores; minimum detected CDM thicknesses ranged from 10 to 35 cm. 



• The areal distribution of both pseudo-UDM and CDM, measured using 

 sediment-profile photography and cores, was relatively consistent with the 

 DAMOS Capping Model. Because of the slope and uneven bottom topography 

 of the area surrounding the primary depositional basin, the material thickness 

 appeared patchy and therefore difficult to reliably contour using only 

 bathymetric methods. 



• The Royal River data indicated two factors that were important in determining 

 sediment tracers that could be used to distinguish die upper and outer reaches: 

 the distribution of the biological components consistent with coastal zonations, 

 and the relative hydrodynamic energy of the river reach. 



• No single tracer was found that was both unique to one reach of the river, and 

 commonly observed in all collected samples, so the method of combining 

 several parameters was found to be most promising at classifying the material 

 types. Limiting the fine fraction analysis to components that have the narrowest 

 range in the dredging area would serve to both decrease the effort required to 

 analyze the samples, as well as increase the statistical reliability of sample 

 identification using tracers. 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



