EXECUTIVE SUMMARY (continued) 



the formation of a conical pseudo-UDM deposit approximately 1.2 m high with flanks 

 extending up to 250 m from the central point of disposal, and a 20 cm cap. Although the 

 volume of cap material was smaller than for normal projects (generally a minimum 

 thickness of 50 cm), the areal distribution of both pseudo-UDM and CDM observed in the 

 demonstration, was relatively consistent with the model predictions. 



An important component of the Portland Disposal Site Capping Demonstration 

 Project was the identification of tracers within the Royal River that could be used to 

 identify the sediment on the seafloor at the PDS. Prior to the excavation of sediment, 30 

 vibracores from three reaches (upper, middle, and outer) of the Royal River were collected 

 and analyzed for a variety of potential tracers. Although no single tracer was identified 

 that was both unique to one reach of the river and commonly observed in all collected 

 samples, a statistical method of combining several biological and mineralogical parameters 

 was found to be suitable for classifying the material types. The sediment fine fraction (63- 

 500 ^m) was selected as providing the most statistically robust data. 



Monitoring at the Royal River Project Area in the southeast comer of the PDS 

 utilized standard DAMOS techniques, including single-beam bathymetry, side-scan sonar, 

 REMOTS® sediment-profile images, as well as grab and core sampling. Results of the 

 monitoring surveys showed that a discrete dredged material mound was detected on the 

 seafloor within the Royal River Project Area. An accumulation of pseudo-UDM was 

 detected to the south and southeast of the disposal buoy position, located in the relatively 

 flat-bottomed basin targeted for disposal. Accurately detecting dredged material deposition 

 in the surrounding area of more complex topography by single-beam bathymetry alone was 

 complicated by survey artifacts. In this case, sediment-profile images and core data were 

 key to mapping the footprint of both UDM and CDM on the seafloor. 



The grab and core samples collected from the disposed dredged material were 

 analyzed for the environmental tracers selected after analysis of Royal River Cores. The 

 statistical tracer data were able to show a discernible difference between the CDM, pseudo- 

 UDM, and ambient material. The presence of historical dredged material at the project 

 area complicated the analyses, as historical material shares biological characteristics with 

 both native, ambient sediment (recolonization by benthic species, settling of planktonic 

 species), and with recent dredged material (presence of freshwater species). 



Statistical analyses showed that tracers successfully identified disposed dredged 

 material layers collected from different regions of the estuary, but material from the 

 middle reach had many overlapping characteristics that complicated the interpretation. The 

 biological indicators were found to be more statistically robust than the mineralogical 

 indicators. Differences in species composition of the microorganism populations 

 corresponded to the contrasts among the brackish habitats of the three reaches of the Royal 

 River. The statistical overlap of the pseudo-UDM and CDM samples collected in cores 



