102 



(insect parts, plant fragments, etc.)- However, this layer did have the highest abundance 

 of planktonic diatoms, dark minerals, and rock fragments. Smooth and texmred ostracods 

 were rare, and flyash, fibrous minerals, plant fragments, and pellets were all very rare. 



Similar to the grab samples obtained over the pseudo-UDM deposit in November 

 1996, the pseudo-UDM layer within the cores had a high abundance of plant material, 

 black porous materials, and planktonic diatoms (Figure 4-28). Dark minerals, rock 

 fragments, smooth and texmred ostracods, and pellets were conmionly present in samples, 

 but in lesser concentrations. Flyash, fibrous minerals, insect parts, benthic diatoms, and 

 shell fragments were rare. Although very rare, gastropod and bryozoan fragments were 

 identified within the fine fraction. 



The CDM layer had a noticeably coarser grained material in the fine fraction, as 

 well as an abundance of black porous material. Flyash, fibrous minerals, and plant 

 fragments were all common. Textured ostracods and pellets were present. Dark minerals, 

 rock fragments, insect parts, smooth ostracods, and shell fragments were rare. Benthic 

 diatoms and bryozoan parts were very rare. 



Microfossils. The mean relative abundance of the five microfossil groups 

 (freshwater thecamoebians, marsh foraminifera [agglutinated], mudflat foraminifera 

 [calcareous] , shelf agglutinated foraminifera, and shelf calcareous foraminifera) was 

 calculated for each sample. The relative abundance is the acmal number of individuals 

 counted per sample divided by the total number of individuals. Because the abundance 

 values are relative values, the population density, in units of numbers of microfossils per 

 gram of sediment, also were used to characterize the layers within the cores. Results from 

 individual cores are provided in Appendix B, and full histograms for each core are 

 provided in Appendix D. 



After the microfossil analysis, using the classification defined from the visual core 

 descriptions, the average relative abundance for each layer (CDM, pseudo-UDM, and 

 ambient (AMB) was calculated. As discussed below, several samples were re-classified 

 after microfossil analysis, so that the final values for mean abundance were calculated 

 using a total of 41 samples: five for AMB, 19 for pseudo-UDM, and 17 for CDM. 



The AMB samples had the highest mean abundance of shelf agglutinated 

 foraminifera (74%) and shelf calcareous foraminifera (13%), and the lowest relative 

 abundance, and density, of all the other groups (Figure 4-29 A). Samples from both Cores 

 C and G contained marsh foraminifera in samples collected from AMB. In Core C, the 

 top two samples of the ambient layer, 26 cm to 44 cm deep, contained over 80% shelf 

 foraminifera in each sample. The samples were reclassified as ambient, rather than 

 pseudo-UDM as in the original core descriptions, but may acmally have represented 

 historic dredged material. The presence of historical dredged material within the project 

 The Portland Disposal Site Capping Demonstration Project, 1995-1997 



