705 



boundaries to some extent complicated the interpretation of the monitoring data (Section 

 5.0). The top AMB sample in Core G contained a small amount of thecamoebians and 

 mudflat and marsh foraminifera in the AMB unit at a depth of 31 to 57 cm. 



The pseudo-UDM samples from the postcap cores had the highest mean value of 

 freshwater thecamoebians (19%), with a range of 7% to 35% (Figure 4-29A). The 

 average was consistent with data collected from the grab samples, which had the second 

 highest thecamoebian content (approximately 15%). The density of the thecamoebians was 

 also highest in the pseudo-UDM (18.7 per gram), relative to 4.8 per gram in the CDM and 

 approximately 2.0 per gram in the AMB (Figure 4-29B). The deepest sample in Core A, 

 collected from approximately 55 cm down in the core, resulted in over 20% thecamoebians 

 and no shelf foraminifera, so although this sample was originally classified as ambient 

 during core descriptions, the sample was re-classified as pseudo-UDM. The appearance of 

 this material, described as ambient, suggested that the sample may actually be historical 

 dredged material, rather than dredged material associated with this project. 



Both the UDM core and grab samples had a small percentage of shelf calcareous 

 foraminifera, but no shelf agglutinated foraminifera. Shelf calcareous foraminifera were 

 also noted in the CDM, but with a smaller relative abundance. Just above and below the 

 CDM/pseudo-UDM boundary in most of the PDS cores a small percentage (2% to 8%) of 

 shelf foraminifera were present. The presence of shelf foraminifera in both pseudo-UDM 

 and CDM material may have originated from the source areas, as small numbers of shelf 

 species were noted in the Royal River cores. However, due to their presence in the grab 

 samples collected from the pseudo-UDM mound, the occurrence of shelf species also may 

 have resulted from recolonization of the surficial sediment layer following disposal. 



The CDM layer contained a higher percentage of both marsh and mudflat 

 foraminifera than the pseudo-UDM layer, and had the lowest abundance (< 1%) of shelf 

 calcareous foraminifera. Overall, the top CDM sample had the highest abundance of 

 foraminifera. The abundances of foraminifera appeared to decrease with depth within each 

 layer. The density of foraminifera was slightly higher in the CDM than in the pseudo- 

 UDM. The greatest abundance of foraminifera occurred consistently in the top CDM or top 

 pseudo-UDM core sample, suggesting similarity in material composition and origin or 

 recolonization. 



Upon processing, the stratigraphy of three cores (B, F, and H) appeared slightly 

 dismrbed and waterlogged. Although a detectable CDM/pseudo-UDM interface was visible 

 in Core B, a small percentage of shelf foraminifera occurred in all four samples which 

 indicated possible mixing of layers during core retrieval or transport. Core H2 was very 

 short (20 cm), and did not have a clear division of dredged material layers based on 

 microfossil content. Because of the clear dredged material layers. Core B was incorporated 

 into the statistical analysis (Section 4.7), but Cores F and H were excluded. 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



