the material had apparently consolidated approximately V2 ft. One week later (14 July), the 

 range of depths in the cell was still relatively narrow (approximately 47.5 - 50 ft), but the 

 deposit showed an average depth of approximately 49.5 ft, indicating an overall consolidation 

 of approximately 1 ft over a period of one week. 



1.2.3 Capping Operations 



Capping operations were conducted from 14 July to 25 July 1997. Sand was slowly 

 placed in the cell using a split-hull scow that was cracked open to slow the rate of material 

 deposition. Disposal operations were conducted only during the outgoing tidal cycle. The 

 scow was positioned using differential GPS (DGPS) in eight locations over the cell for a 

 total volume of 14,800 yd^ (Appendix; ENSR 1997a; NAE 1997). The sand was obtained 

 from Ossippee Aggregate. Grain size ranges of the sand were reported as dominated by 

 coarse sand (59%), with smaller fractions of gravel (15%), and fme-medium sand (23%; 

 grain size classifications from Wentworth 1922). 



A bathymetric survey was conducted after seven loads of material were placed with 

 the scow oriented in north-south positions around the cell (Appendix). The bathymetric data 

 showed a large mound in the center of the cell. Modeling conducted prior to capping using 

 tidal current data predicted that the sand would spread towards the south (down current) 

 during sand disposal. The preliminary bathymetric data showing a flat, well defined 

 sedunent surface was interpreted as indicating that the sand coverage in the southern end was 

 well distributed (resulting from settling from the southerly tidal current), but the northern 

 end of the cell was insufficiently covered. To rectify this, the contractor first unsuccessfully 

 used a sweep bar to even the coverage, and then used a clamshell bucket to redistribute the 

 material. Three 80-ft wide cuts were dredged from the central portion of the cell, and the 

 material was placed in the northern end of the cell. Following this operation, a final barge 

 of sand was placed in the cell; this scow was positioned along an east- west orientation in the 

 northern section of the cell for the final cap disposal event. Weeks Marine conducted a final 

 postcap bathymetric survey at the end of the project on 25 July 1997. 



1.3 CAD Cell Monitoring Survey 



Following completion of the cell, NAE and Massport were planning on accelerating 

 part of the monitoring required by the Water Quality Certificate. Coincidentally, samples 

 collected as part of a separate research project suggested that part of the cell contained 

 insufficient cap material (Shull and Fitzgerald 1997). Using this information and 

 recommendations of the technical advisory committee (TAC), NAE planned and 

 implemented an acoustic and coring survey as part of the Water Quality Certificate 

 monitoring to assess the success of capping of the first CAD cell, and to provide a resource 

 for operational and monitoring modifications for application to the remainder of the 

 BHNIP. In addition to the acoustic and coring survey, a follow-up video survey was 



MONITORING RESULTS FROM THE FIUST BHNIP CONFINED AQUATIC DISPOSAL CELL 



