28 



sediment matrix. REMOTS® photographs revealed thin surface sand overlying silt/clay 

 sediments at several stations within the disposal site. A similar sand-over-mud layering was 

 observed at several stations in the 1991 survey. 



Stations F300S, F400S, and F200SW (located on the ridge in the southeast portion of 

 the survey) exhibited surface cobble layers. Cobble was considered to be the ambient 

 sediment type for the ridge although it might also have originated as dredged material. 

 Consolidated clay material at stations adjacent to the WLIS "E" and "F" mounds (Figures 3- 

 &4 and 3-11) was clear evidence of dredged material. Consolidated clay material is resistant 

 to erosion and can persist for several years until sufficient biogenic activity breaks down 

 clumps and incorporates the clay into the sediment column. At the tops of disposal mounds, 

 shell lag is often exposed after the winnowing of unconsolidated, fine silt/clay material. The 

 surface shell layer at F300N (located on the WLIS "E" mound) provided evidence of this 

 winnowing process. This shell layer can protect the mound from further winnowing of 

 material and contribute to the stability of the mound. 



Reference areas 2000W and EAST consisted primarily of silt/clay sediments whereas 

 sediments at the newly selected SOUTH reference area consisted of very fine sand (Figure 3- 

 12). REMOTS® photographs revealed consolidated clays and surface shell layers at some 

 stations within the EAST reference area. A similar surface shell layer was evident at some 

 stations in the 1991 reference area, WLIS-REF. 



During the 1992 REMOTS® survey, reference area 2000S exhibited fine sand 

 sediments (2-3 phi). The 3-4 phi (very fine sand) grain size of the SOUTH reference area 

 resembled more closely the sediment grain size of the on-site ambient stations and, therefore, 

 was a more appropriate sediment type to be compared with sediment conditions in 1992. 



3.2.3 Boundary Roughness 



Twenty-four of the twenty-five disposal site stations had mean boundary roughness 

 values between 0.6 and 1.9 cm (Figure 3-13). Observed boundary roughness was attributed 

 to physical (as opposed to biogenic) processes. The 1991 on-site data displayed a similar 

 distribution: 20 of 25 stations had mean boundary roughness values between 0.6 and 1.4 cm. 



Thirty-six of the thirty-nine reference stations sampled at all three reference areas 

 exhibited mean boundary roughness values < 1.9 cm for the 1992 survey compared to 31 of 

 39 stations for the 1991 survey (Figure 3-14). Eight of the REMOTS® stations occupied in 

 1991 had boundary roughness values greater than 1.8 cm. These larger values were 

 attributed to sand waves at the 2000S reference area. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1992 



