97_ 



surficial sediment layer (Figure 4-26A). RPD depths ranging from 1 to 3 cm and the 

 presence of several infaunal deposit feeding worms in the sediment-profile photographs 

 indicated a healthy benthic recolonization of the dredged material (Figure 4-26B). 



4.5.3 Sediment Coring 



We obtained nine sediment cores from the Royal River mound during the CDM 

 survey to provide a cross section of the CDM, pseudo-UDM, and ambient sediments 

 (Figure 4-27). Each core was split, described, and analyzed to both supplement and verify 

 the bathy metric and REMOTS® sediment-profile photography results. The recovered 

 sediments were sub-sampled relative to visible sediment horizons, preserved, and analyzed 

 for grain size and mineralogical composition, as well as microfossil content. 



4.5.3.1 Visual Core Descriptions 



As detected in the REMOTS® photographs, the CDM/pseudo-UDM interface was 

 marked by a sharp change in sediment grain size. Although the dark, olive green to black 

 color of the sediments was consistent throughout, a distinct boundary between the two 

 sediment layers was detected in six of the nine cores collected. The thickness of CDM 

 ranged from 9 cm in Core G2 to 36 cm in Core E6. Cores F2 and H2 were excluded from 

 analysis, because the cores yielded only a small volume of material which increased the 

 likelihood of disturbance during retrieval. 



Ambient sediments, characterized as a medium-grained sand (1.0 to 2.0 phi), were 

 recovered in the bottom of Cores A9 and G2. A similar tan, sandy component was 

 collected near the bottom of Core CI. However, the material in CI appeared to be 

 stratified by grain size and emitted a strong smell of hydrogen sulfide (HjS), possibly 

 linking it to the sewer outfall in Royal River or the 1995 improvement dredging project at 

 a marina in the Harraseeket River. Shell and wood fragments were found throughout all 

 nine sediment cores. Complete descriptions and graphical representations based on the 

 visual descriptions of the CDM sediment cores can be found in Appendix C. 



4.5.3.2 Core Grain Size Analysis 



An analysis of the ranges of grain size was made based on the visual material 

 classifications (Section 4.5.3.1). In general, grain size analysis of the samples extracted 

 from Cores A9 through II supported the presence of three distinct layers of material 

 (CDM, pseudo-UDM, and ambient) over the disposal mound (Table 4-7). These data are 

 evaluated below, and compared with the grain size data collected in the grab samples 

 collected following placement of the pseudo-UDM. 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



