101 



Samples identified as being collected in CDM and extracted from the top sections of 

 the cores collected after cap material was placed tended to contain a relatively high sand 

 fraction, with a mean percent composition of 56% (Figure 4-18). In general, the average 

 silt (30%) and clay (13%) content of the material classified as CDM were lower than the 

 average measured values in both the material classified as UDM in the cores (50% and 

 22% silt and clay, respectively), and in the UDM grab samples (49% and 23%, 

 respectively). However, the top CDM samples of Cores CI, E6, and A9 had grain sizes 

 more comparable to the pseudo-UDM than the average CDM sample. This discrepancy is 

 likely due to the deposition of the finer grained material from the middle zone of the river 

 over the initial sandy CDM layer. The clay fraction of both the UDM samples from the 

 cores and grab samples was consistently around 20%. 



Some discrepancies in these trends of grain size were noted. In the lower part of 

 Core B (24 cm to 31 cm), the percentage of sand (56%) within the layer classified as 

 pseudo-UDM was exceptionally high, probably due to the incorporation of some amount of 

 ambient material. Sand was also the dominant component in the lowest pseudo-UDM 

 sample of Core A9 (ambient origin) and in the top pseudo-UDM sample of Core E6 (CDM 

 origin). These discrepancies were evaluated further during statistical analyses. 



The ambient samples were composed dominantly of sand (73 %). Silt had a 

 significantly lower abundance (13%) than observed in both the pseudo-UDM and CDM 

 layers. The low percentage of clay (14%) in the ambient material was comparable to the 

 average measured in samples classified as CDM (13%). One sample from the 26 cm to 30 

 cm horizon in Core CI, classified as pseudo-UDM (or possibly ambient) in the visual 

 descriptions, had an unusually low percentage of sand (26%). 4. 5. 3. 3 Fine Fraction 

 Analysis 



In eight of nine cores, distinctions between the CDM, pseudo-UDM, and ambient 

 material were apparent based on mineralogical composition and microfossil assemblage and 

 density. 



Mineralogy. The mineralogical analysis of the fine fraction (63 ^m to 500 ^m) for 

 the 41 samples extracted from seven of the nine PDS gravity cores indicated the 

 composition of the sediments was predominantly quartz, with micas common. The 

 mineralogical abundance of 16 other components of the Royal River sediment samples was 

 used to assist in the differentiation of the three sediment layers. 



The fine fraction grain size was determined to be medium-coarse for the ambient 

 and pseudo-UDM layers and coarse for the CDM layers (Table 4-8; Figure 4-28). Due to 

 the homogeneous namre of the material and differences in sedimentation processes, the 

 ambient layer had the lowest overall abundance of mineralogic and biologic components 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



