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The sediment composition and microfossil content of the ambient material prior to 

 disposal of Royal River sediment was not studied. An overall description of the material, 

 however, was reliably obtained from the samples collected in the postcap cores. In the 

 ambient samples, shelf foraminifera composed about 83% of the relative abundance in the 

 ambient layer samples. The ambient layer also had a high abundance of planktonic 

 diatoms, pellets, dark minerals, and rock fragments. 



Only two cores recovered sediment that was given a final characterization as 

 ambient material (C and G). Both of these core sections had a small component of mudflat 

 and marsh foraminifera. These brackish and freshwater microfossils in the ambient 

 sediment suggested the presence of some historic dredged material. The marsh 

 foraminifera, sorted sand, and the strong sewer smell in the ambient samples of Core C 

 also provided indications of historical dredged material deposition. 



Another sample possibly encountering historical dredged material was the deepest 

 sample in Core A, collected approximately 55 cm from the top of the core. This sample 

 contained over 20% thecamoebians and no shelf foraminifera characteristic of ambient 

 sediments in PDS. Because the sample did not have the typical texmre of dredged 

 material, the sample was originally classified ambient during core descriptions; following 

 microfossil analysis the sample was reclassified as pseudo-UDM. The ambient appearance 

 of this material and the presence of shelf foraminifera in the 48 to 52 cm sample, however, 

 suggested that the sample may actually be historical dredged material, rather than dredged 

 material associated witii the Royal River project. 



Several of the grab and core samples classified as pseudo-UDM indicated the 

 presence of shelf foraminifera. Although three Royal River cores (RR-26 and RR-18 from 

 the 1995 analyses; as well as RR-6 from the summer 1997 analyses) indicated the rare 

 presence of shelf foraminifera, the shelf foraminifera in the pseudo-UDM were relatively 

 more abundant. It is likely that rapid recolonization of shelf species occurred after disposal 

 events. Previous recolonization studies suggest that benthic calcareous foraminifera re- 

 populate dredged material deposits soon after disposal, and increase in abundance with 

 time (Rhoads et al. 1977). 



A few of the calcareous species identified at the PDS were planktonic and live 

 floating in the water. Planktonic species may descend through the pelagic environment and 

 settle on the sediment surface or be capmred and transported with disposed dredged 

 material. Most foraminifera detected in the sediment samples were benthic species 

 suggesting that recolonization was more common than surface contamination. The 

 prevalence of planktonic diatoms in most core and grab samples as well as the top samples 

 of the ambient layers, yet absence in Royal River samples, also indicated surface 

 contamination by planktonic species in the dredged material at the disposal site. 

 The Portland Disposal Site Capping Demonstration Project, 1995-1997 



