49_ 



perfection of this disposal and containment technique allows NED to deposit moderate to 

 large volumes of UDM, while requiring a minimum investment of CDM. 



The strategic repetition of precision bathymetric, REMOTS®, and geotechnical 

 coring surveys was invaluable during the New Haven Capping Project. The five separate 

 datasets allowed SAIC to document the progression of CAD mound development and 

 advise NED upon the best course of action to achieve its ultimate goal. The results of each 

 bathymetric survey provided a "snapshot" in time, allowing comparisons with previous 

 surveys to document and quantify central mound consolidation, calculate overall growth of 

 the CAD mound, and identify areas requiring additional cap material deposition. This 

 comprehensive dataset also facilitates revisiting the various stages of the capping project to 

 chronicle how disposal and oceanographic processes affected the dredged material, as well 

 as to explore what knowledge of CAD mound construction was gained. 



During the baseline survey, REMOTS® sediment-profile photography was used to 

 estimate the shear strength, as well as document the successional status of the containment 

 ring. The flanks of the UDM mound were mapped by REMOTS® within the containment 

 basin during the precap survey of the NHAV 93 mound. These data were used to ensure 

 accurate placement of the dredged material during disposal operations and permit the 

 calculation of target capping points along the mound apron (Figure 4-6). REMOTS® 

 photography continues to be used to detect changes in various physical and biological 

 parameters on the surface of the NHAV 93 mound. 



The surface layer shear strengths of the five mounds sampled during the baseline 

 survey indicated that significant de-watering and consolidation had occurred in the surface 

 sediments. The larger grain-sized and densely packed sediment deposits displayed higher 

 shear strengths, indicating the potential to contain a ridge of new dredged material while 

 maintaining the mound integrity. No structural failure was detected within the seven- 

 mound containment ring during any of the five bathymetric surveys. 



URI estimated the relative consolidation of sediments occurring between the precap, 

 interim cap, and postcap surveys using both theoretical models and data from the 

 geotechnical cores. These estimates were required to determine cap material requirements; 

 actual cap thickness was masked by consolidation of both the basement material (ambient 

 sediments and historic dredged material) and the UDM deposit. Cores collected 

 immediately following the construction of the mound included the basement material, 

 UDM, and CDM. Results were used to establish the initial geotechnical characteristics of 

 the completed mound. These data were used as a reference for future geotechnical and 

 bathymetric surveys. Numerical computations will also be performed on settlement and 

 volume changes. 



Monitoring Surveys of the New Haven Capping Project, 1993-1994 



