24 



2.2.6 Capping Dredging Operations, Fall- Winter 1996-97 



After the precap survey in mid-November, capping operations began. Because the 

 outer reaches originally designated to serve as CDM were previously dredged and 

 deposited at the DG buoy, the project design had to be modified. The dredge was moved 

 from the anchorage area and positioned near the mouth of the Royal River to obtain 

 capping material distinct from the pseudo-UDM. Dredging operations proceeded up the 

 river, with barges loading sediments from the middle section and transporting them to the 

 PDS. The sandy sediments near the outer reaches of the river were placed over the 

 pseudo-UDM deposit as the first layers of cap. In cross-section, the horizon of higher 

 sand content material serves as an indicator of the CDM/pseudo-UDM boundary. Later 

 layers of capped material originated from the middle section of the river to the border of 

 the upper reaches that were dredged for pseudo-UDM. From November 21 to December 

 23, 1996, the clamshell bucket dredge supplied an estimated barge volume of 22,200 m^ of 

 CDM dredged from the middle and outer channel reaches (Figure 2-9). 



2.2.7 Royal River Project Area Postcap (CDM) Survey 



Following the final completion of CDM material placement, SAIC conducted a 

 postcap survey in mid- January 1997 consisting of precision bathymetry and REMOTS® 

 sediment-profile photography to verify accurate placement of the cap material (Figure 2-6) . 

 In addition, a series of nine gravity cores were collected over the Royal River mound in 

 early February to obtain cross sections of the capped mound and examine the boundary 

 between the pseudo-UDM and CDM layers. 



2.2.8 Additional Analysis of Royal River Sediment Cores 



The area between the upper and middle reaches of the Royal River, where the areas 

 dredged for pseudo-UDM and CDM intersect (Figure 2-9), was identified as an important 

 area of interest as the cores from the smdy area were analyzed. The area between Cores 

 RR-15 and RR-26 (Figure 2-4) was not studied in detail during the preliminary Royal 

 River core analysis. To clarify the lithological and biological characteristics of this key 

 transitional area, three more cores from the Royal River were processed and analyzed in 

 the summer of 1997. Cores RR-6, RR-5, and RR-3 were selected from the Royal River 

 archived cores and processed, providing additional evidence for interpretation of cores 

 collected both from the Royal River and the project area (Figure 2-9). 



2.3 Capping Model Predictions 



Based on the amount of dredged material disposed at the PDA buoy during the 

 Portland Capping Experiment (39,500 m^ pseudo-UDM and 22,200 m^ CDM), the 

 The Portland Disposal Site Capping Demonstration Project, 1995-1997 



