16^ 



The USAGE performed a preliminary pre-dredging survey from the base of the falls 

 to the mouth of the Royal River consisting of a bathymetric survey and the collection of 12 

 sediment characterization cores (Al through E3; Figure 2-4). Analysis of bathymetric data 

 yielded sediment volume estimates of 73,000 m^ to be removed from the channel and 

 anchorage area, in order to provide safe navigational depths at low tide (Figure 2-5). 

 Testing of the sediments collected in Cores A-1 through E-3 indicated that all the material 

 to be dredged from the river basin was suitable for unconfined open water disposal or for 

 beneficial use projects and classified as CDM. 



This moderate volume of high quality sediment was ideal for the capping 

 demonstration project at PDS. The Royal River dredged material for the Portland Disposal 

 Site Capping Demonstration Project presented no enviroimiental risk. Because the 

 sediments throughout the riverbed were determined to be suitable for open water disposal, 

 the inability to successfully construct a capped mound consisting of two distinct layers 

 would have no adverse environmental or ecological impact. Initial baseline smdies in 

 support of the capping demonstration project began in August 1995, and monitoring 

 continued through February 1997, as the capped mound was formed within a basin feamre 

 on the PDS seafloor at a depth of 64 m (Figure 2-6). Because of the complexity of the 

 timing of dredging and monitoring operations, the details of the time line presented in 

 Figure 2-6 are provided in Section 2.2. 



2.2 Capping Demonstration Project Time Line 



2.2.1 Baseline Surveys at the Royal River and Royal River Project Area 



In August of 1995, SAIC collected 30 vibracores (RR-1 through RR-30) from three 

 reaches (upper, middle, and outer) within the Royal River navigational channel to 

 supplement data acquired from 12 cores collected by NAE (Figure 2-4). The cores 

 provided deep cross sections (up to 3 m) of the riverbed and allowed for the identification 

 of several tracers within the project sediments capable of tracking dredged material from 

 its origin in the river, to the disposal mound on the PDS seafloor. 



Detailed analysis of 11 of the 30 sediment cores indicated both microfossils and 

 mineralogical components in the sediment could be used to identify source material 

 removed from the upper and outer reaches of the river (Figure 2-4). The most promising 

 technique was the determination of assemblages of two informal grains of unicellular, 

 eukaryotic microorganisms (Foraminifera and Thecamoebina). These organisms form hard 

 shells, which may be preserved during the natural accumulation of sediment in the river. 

 As a result, these shells can be examined in the dredged material and used to recognize the 

 environment of the original deposition. Differences in species composition of the 

 microorganism populations would correspond to the contrasts between the freshwater 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



