23 



collected very near the cell wall. Core recovery was greater in the cores collected 

 throughout most of the day in the southern area and along the edges where there was little 

 to no sand. The outside of the barrels of the last two cores which were not recovered 

 because of stuck core barrels (6C and 7 A) returned covered with sand, indicating that core 

 recovery was hampered by thick sand intervals. 



There were three distinct units recovered in the cores. The most common was a 

 black silty clay/clayey silt with a strong hydrocarbon odor. The texmre ranged from very 

 watery silt to highly consolidated, low water content firm clay. The second end member 

 unit was a brown medium to coarse sand. Finally, several cores penetrated into a 

 continuous interval of well consolidated BBC. When the core penetrated to refusal into the 

 BBC material, we assumed the core had penetrated into the bottom of the cell. Comparing 

 total dredged material thicknesses as recovered in the cores with bathymetry suggested that 

 core recovery was hampered by loss or compaction of dredged material during the coring 

 process. In Table 2-1, a fourth unit was described as "Mixed," which was commonly 

 medium to coarse sand with a component of black watery silt material, apparently from the 

 dredged material unit. These units were described in order to estimate the potential 

 magnitude of mixing between sand and dredged material. 



The dredged material unit was mottled with BBC in many cores, and in one core 

 (CAD-5A), a solid 15 cm interval of BBC was recovered above the dredged material. The 

 presence of BBC in the dredged material was consistent with reports from on-site 

 inspectors. In addition to BBC, discrete sandier intervals were also noted in the dredged 

 material. Data from cores collected prior to capping indicated that the dredged material 

 consisted of up to 30% sand. For classification purposes, if the sand was a minor 

 component of the dredged material, and disseminated throughout an interval, it was 

 classified as dredged material. If the unit was dominated by medium-coarse sand but was 

 infused with black watery silt material, it was classified as mixed. 



The two replicate cores collected at CAD-2, CAD-3, and CAD-4 recovered no 

 sand, and all but CAD-4B were cored to refusal in BBC. These results indicated that no 

 sand was placed in the southern section of the cell. Cores CAD-IA and IB (Figure 3-6) 

 were collected near the sand/mud boundary, and the results indicated that, near the sand 

 cap boundary, limited mixing of sand and mud resulted in interleaved layers of sand and 

 mud in these cores. The subbottom data also indicated that a wedge of sand near the edge 

 of the sand cap may have been intermixed with the more fluid mud, hampering acoustic 

 differentiation between these lithologies (Section 3.4). 



Cap thicknesses among the four cores where sand cap was clearly recovered at the 

 top of the core (CAD-5A, 5B, 6A, and 6B) ranged from 20-28 cm. In cores CAD-5A and 

 5B, the boundary between the sand cap and the underlying material was sharp and clearly 

 delineated due to the presence of consolidated clays below the sand (Figure 3-6). The 

 stratigraphy was uncertain at core CAD-6A (45 cm of recovery), because material was lost 



MONITORING RESULTS FROM THE FIRST BHNIP CONFINED AQUATIC DISPOSAL CELL 



