additional information other than to verify results obtained from 

 the precision bathymetric survey. 



3.1.3 Surface Textural Characteristics 



Sediment samples taken for grain size and chemical 

 analyses at the Brenton Reef site (Figure 2-4) were not analyzed 

 but archived at the NED laboratory. However, an accurate 

 characterization of surface sediment textures at the site is 

 possible based on the REMOTS® survey results. The REMOTS® 

 photographs indicated historically-deposited dredged material in 

 the western quadrant of the disposal site which extended 

 approximately 500 meters beyond the western disposal site boundary 

 (Figure 3-4) . This material occurred at some stations in a 

 distinct layer from 3 to 12 cm thick and occupied an area having an 

 east-west diameter of roughly 1300 meters and a north-south 

 diameter of about 2000 meters. 



The sediments comprising the historic deposit showed a 

 range in grain-size from very fine sand (4-3 phi) to granule and 

 larger (< -1 phi) (Figure 3-5) . For example, at station E-6 near 

 the center of the deposit, both medium sand (2-1 phi) and granules 

 (-1 to -2 phi) were found to exceed the depth of prism penetration 

 in replicate images (Figure 3-6) . At other stations located near 

 the center of the mound and at those on the flanks of the mound, a 

 sand-over-mud or cobble-over-mud stratigraphy was noted (Figure 3-7 

 A and B) . Penetration of the camera was prevented by large cobbles 

 at station E-5, located just north of the disposal mound apex. 



The obvious gradations in the grain size of surface 

 sediments at the Brenton Reef site, from coarse cobble to sand, 

 sand over mud, and mud were the result of both historic dredged 

 material deposition patterns as well as near-bottom kinetic 

 regimes. Cobbles and coarse sands at stations closest to the mound 

 apex (Figure 3-6, bottom image) reflected a higher-energy 

 environment which may be related to the elevation of the mound 

 above ambient depths. At such stations, it is likely that finer- 

 grained fractions had been winnowed and redeposited on the flanks 

 of the mound, resulting in the observed pattern of sand over mud 

 stratigraphies at flank stations (Figure 3-7 A and B) which in turn 

 grade into silt-clay as distance and depth from the mound peak 

 increases. Shell lag deposits (Figure 3-8) and near-surface sands 

 (Figure 3-9) provide evidence of the winnowing of fines in response 

 to erosional forces near the mound apex. These results are 

 comparable to those obtained in the 1978 bathymetric survey at 

 Brenton Reef, when the top of the disposal mound was described as 

 having a sand surface layer covering silty dredged material, and 

 the mound flanks had exposed mud (Naval Underwater Systems Center, 

 1979) . 



