1.0 INTRODUCTION 



Dredged materials unsuitable for 

 unconfined open water disposal have been 

 managed through a variety of confinement 

 techniques. In 1979, the New England 

 Division of the Army Corps of Engineers 

 pioneered an approach to place unsuitable 

 materials on discrete areas of level ocean 

 floor and "cap" these materials with 

 dredged materials suitable for unconfined 

 disposal (for a review see Murray et al. 

 1992). This approach has been used by 

 other Corps Divisions (Sumeri et al. 1991) 

 and employed with success in water depths 

 up to 60 m. 



This paper reviews and summarizes the 

 available information on open water 

 disposal of dredged material that is 

 pertinent to proposed capping projects. 

 This information includes the behavior of 

 the material as it falls through the water 

 and evidence collected from monitoring 

 disposal activities in both shallow water 

 (<25 m) and deeper water (>25 m). The 

 ability to monitor both the formation of the 

 mound and the placement of the cap has 

 been critical in developing successful 

 capping techniques in shallow water 

 (Murray et al. 1992). The experience 

 gained, and the information gathered, in 

 these operations will be applied to an 

 evaluation of the potential for success in 

 deeper water. 



While there is no evidence that capping 

 cannot be accomplished in greater depths of 

 water, several concerns have been raised 

 regarding proposals to extend the depth of 

 capped disposal operations (e.g., Dolin and 

 Pederson 1991). There is concern that the 



increased water depth will present logistical 

 problems, contribute to wider dispersal of 

 unsuitable sediments, and lead to poor 

 control over placement of cap sediments. 

 These issues focus on the apparent lack of 

 experience with dredged material behavior 

 in deeper water and preliminary evidence 

 that disposal activities in deep water failed 

 to produce discrete mounds (SAIC 1984a). 



To cap unsuitable sediments effectively, 

 two primary goals must be achieved. First, 

 the unsuitable sediments must be placed in 

 a discrete mound on the ocean floor 

 without extensive spreading or dispersal 

 into the water column. Acceptable limits to 

 spreading of the initial mound are defined 

 by the amount of cap sediments available. 

 Acceptable limits to dispersion in the water 

 column are defined in the United States 

 Ocean Dumping Regulations (Title 40, 

 Code of Federal Regulations, Parts 227-8). 

 Second, the cap sediments must be placed 

 accurately so that they completely cover the 

 mound without disturbing the unsuitable 

 material. There is ample evidence in 

 various open ocean disposal projects that 

 sediment can be placed accurately on the 

 seafloor (e.g., SAIC 1990a, 1991, Murray 

 et al. 1992). 



The Massachusetts Bay Disposal Site 

 (MBDS) is primarily where concern 

 regarding depth and the use of capping has 

 been an issue. Specifically, the proposed 

 Boston Harbor Navigation Improvement 

 Project will require the dredging of an 

 estimated 2.2 x 10 m 3 of sediment from 

 the Mystic River, the Chelsea River, and 

 the Reserved Channel. A significant 

 portion of this material (approximately 

 500,000 m 3 ) is estimated to be unsuitable 



Deep Water Capping 



