concentrations, this material is classified as unacceptably contaminated dredged material 

 (UDM), requiring special handling, storage, and disposal techniques (Fredette 1994). 



One cost-effective and environmentally sound alternative for large scale dredging 

 projects is to dispose of the UDM at open water disposal sites monitored by the DAMOS 

 Program, and cover the initial deposit with a larger volume of CDM. Capping is a 

 subaqueous containment method that uses CDM to overlay and completely cover a UDM 

 deposit, isolating the contaminants from the marine environment (SAIC 1995). Capping 

 was first introduced as a management technique of the DAMOS Program during the 

 1978/79 disposal season with the development of the Stamford-New Haven mounds 

 (STNH-N and STNH-S) at the Central Long Island Sound Disposal Site (CLIS; SAIC 

 1995). Over the past 18 years, monitoring and research activities within the DAMOS 

 Program regarding subaqueous capping of UDM have evolved, resulting in significant 

 progress in pre-project planning and the ongoing development of management strategies. 



A successful capping project depends on the selection of an appropriate disposal 

 site, identification and access to large volumes of CDM, as well as the careful control of 

 dredging and disposal operations. Currently, the DAMOS Program maintains ten closely 

 monitored open water disposal sites along coastal New England capable of receiving both 

 clean and contaminated sediments (Figure 1-2). However, the low kinetic energy 

 envirormient, shallow to moderate water depths (20 m to 22 m), and gently sloping, 

 regular bottom topography have made CLIS the preferred proving ground for innovative 

 dredged material management and disposal techniques. 



Capping operations on a flat or gently sloping bottom usually require a 2:1 to 6:1 

 CDM to UDM ratio to adequately cap a contaminated sediment deposit. An exception was 

 during the 1993/94 disposal season at CLIS, when a capped mound composed of over 

 1,100,000 m^ of sediment dredged from the federal chaimel and active ports in New Haven 

 Harbor was constructed on the seafloor (Morris et al. 1996). The material was placed in 

 the center of an artificial contairmient cell formed by the controlled deposition of small to 

 moderate volumes of dredged material over a ten-year period. The resulting bottom 

 feamre was found to be a broad, stable confined aquatic disposal (CAD) mound with a 

 CDM to UDM ratio of 0.96: 1.0 (Morris and Tufts 1997). The artificial containment 

 measures restricted the lateral spread of the large, strategically placed UDM deposit 

 (590,000 m^), requiring less CDM (569,000 m^) to completely isolate the contaminated 

 material. 



Natural contairmient measures (i.e., basins, bedrock outcrops, terminal moraine 

 deposits, etc.) also can be employed in the development of capped mounds. The pre- 

 existing glacial features of Massachusetts Bay Disposal Site (MBDS), Cape Arundel 

 Disposal Site (CADS), Portland Disposal Site (PDS), and Rockland Disposal Site (RDS) 

 lend themselves for use in subaqueous capping operations. Although significantly deeper 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



