84 



4.4=3.1 Grain Size Analysis 



Grain size analyses indicated that the average pseudo-UDM sample had a 

 comparable grain size to the organic-rich material collected from the upper reaches of the 

 Royal River. The mean grain size distribution for the sediment forming the pseudo-UDM 

 mound was 25% sand, 44% silt, and 21 % clay (Table 4-4; Figure 4-18). For most 

 samples, the percent composition ranged from 31% to 38% for sand, and 40% to 47% for 

 silt, except for samples CTR, 50S, and 50SE which had less sand (11-18%) and more sik 

 (56-63%). The clay content within the mound sediments was consistent with percent 

 composition ranging from 20-26%. 



4.4.3.2 Fine Fraction 



Mineralogy. As in the August 1995 Royal River cores, mineralogical analysis 

 (based on visual description) of the nine pseudo-UDM grab samples showed that quartz 

 was dominant and micas common. Sand-sized particles retained in a 62.5 /xm sieve were 

 classified as medium to coarse (2.0 to 1.0 phi; Table 4-5). Black porous material and plant 

 fragments, in all but the methanol-preserved sample, were common to abundant (Figure 4- 

 19). Insect parts, planktonic diatoms, and pellets were common in nearly all samples. 

 Flyash, rock fragments, as well as textured and smooth ostracods were common in most 

 samples. Fibrous minerals and shell fragments were very rare, and benthic diatoms were 

 absent. 



Microfossils. The pseudo-UDM grab samples contained all five groups of 

 microfossils (thecamoebians and foraminifera: marsh, mudflat, shelf agglutinated and shelf 

 calcareous); Figure 4-20 A). Marsh and mudflat foraminifera were dominant in all 10 

 sediment samples analyzed, while freshwater thecamoebians composed from 5% to 30% of 

 the individuals counted. With the exception of the sample collected at Station CTR and the 

 methanol-preserved sample from 50NE, shelf calcareous species were collected from the 

 surface of the pseudo-UDM deposit (percent abundance ranging from 2% to 20%), 

 suggesting rapid recolonization of the dredged material by shelf species. Two samples, 

 50SE and 50S, contained a few shelf agglutinated species and had a significantly greater 

 density of foraminifera than the other samples (Figure 4-20B). The thecamoebians had a 

 consistent density ranging from 4 to 20 individuals per gram. Foraminifera varied in 

 density, with most samples ranging from 40 to 120 individuals per gram. 



Both samples (methanol and formalin) from Station 50NE were processed and 

 analyzed in order to compare microfossil content. Microfossil analyses determined the 

 sample preserved in formalin solution contained nearly double the density of foraminifera 

 relative to the sample preserved in methanol. After picking five trays of sediment, there 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



