130 



processing, and avoiding sampling from the outside of the core, would help to limit cross- 

 contamination. Finally, longer cores into ambient material would provide more robust 

 groundtruth data on the acmal thickness of dredged material layers. 



5.3.4 Fine Fraction Tracer Technique 



Microfossils. Microfossil analysis proved to be a valuable tool to characterize the 

 sediment composition of the Royal River and trace the dredged material at the PDS. The 

 predominance or absence of shelf species in a sample clearly indicated whether the material 

 was ambient or part of the pseudo-UDM, although the presence of historical dredged 

 material at the site contributed some uncertainty. For a few samples, the classification of 

 pseudo-UDM or ambient layers based on visual observations were re-categorized following 

 the identification of microfossils. The percentage of thecamoebians was important in 

 distinguishing the CDM from the pseudo-UDM. The density distribution of microfossils 

 was also useful in identifying the CDM/pseudo-UDM horizons in the cores. The ratios of 

 agglutinated to calcareous foraminifera and, more specifically, marsh to mudflat 

 specimens, were not effective indicators because the ratios were inconsistent throughout the 

 Royal River regions. Overall, limiting the fine fraction analysis to those components 

 which are most representative of a narrow range in the dredging area (Figure 5-3) would 

 increase the statistical reliability of sample identification using tracers. 



Mineralogy. Overall, mineralogical observations provided a useful supplementary 

 tool to characterize the river regions, dredged material, and ambient substrate. 

 Descriptions of sediment mineralogy on a microscopic level were important for 

 documenting indicators of river regions and using them to trace dredged material. Grain 

 size analysis of the fine fraction alone was not sufficient to distinguish the pseudo-UDM 

 layer from the ambient substrate, both of which had a medium grain size. Because all 

 indicators were mostly rare components of the samples and may have patchy distributions, 

 there is a degree of uncertainty in determining how representative they are of the entire 

 area dredged. In addition, quantification of the data was difficult and not as precise as 

 counting the individual species of microfossils. Duplicate analyses, however, increased the 

 precision of the mineralogy analysis (the two splits of Core RR-3 contained identical 

 mineralogical characteristics). 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



