Disposition of dredged material has become a problem of such proportions that all potential solutions must be explored. The present study was conducted to survey existing knowledge of, inventory, describe, and evaluate the potential for using subaqueous pits, holes, or depressions as dredged material disposal sites. The scope was limited to investigating the estuaries, bays, rivers, and continental shelf areas of the Atlantic, Gulf, Pacific, and Great Lakes coasts of the United States. Included were all subaqueous depressions whether caused by dredging or extraction activities or by natural erosional events. The author concludes that the potential for having or creating man-made subaqueous disposal sites will depend upon demand and supply of the products excavated. Demand for construction aggregate in the vicinity of large coastal metropolitan areas and for shell as a source of aggregate or feed supplement. Adequate supplies for beach replenishment and construction aggregate are presently known or can be reasonably hypothesized, with economic constraints being the only hindrance to widespread usage. Conversely, shell supplies are limited, dredging areas are being curtailed, and the resulting pits fill rapidly. Thus, there is little potential, for shell dredging to leave extensive pits.

Disposition of dredged material has become a problem of such proportions that all potential solutions must be explored. The present study was conducted to survey existing knowledge of, inventory, describe, and evaluate the potential for using subaqueous pits, holes, or depressions as dredged material disposal sites. The scope was limited to investigating the estuaries, bays, rivers, and continental shelf areas of the Atlantic, Gulf, Pacific, and Great Lakes coasts of the United States. Included were all subaqueous depressions whether caused by dredging or extraction activities or by natural erosional events. The author concludes that the potential for having or creating man-made subaqueous disposal sites will depend upon demand and supply of the products excavated. Demand for construction aggregate in the vicinity of large coastal metropolitan areas and for shell as a source of aggregate or feed supplement. Adequate supplies for beach replenishment and construction aggregate are presently known or can be reasonably hypothesized, with economic constraints being the only hindrance to widespread usage. Conversely, shell supplies are limited, dredging areas are being curtailed, and the resulting pits fill rapidly. Thus, there is little potential, for shell dredging to leave extensive pits.

Past underwater sand mining has left many large depressions, called subaqueous borrow pits, on the floor of the Lower Bay of New York Harbor. Research has shown that borrow pits are natural sinks for contaminant-laden sediment and that they contain stressed benthic communities different from those found in nonpit areas. The disposal and capping of contaminated dredged material into borrow pits would obviate possible impacts at the ocean disposal site while reclaiming lost portions of the sandy bottom of New York Harbor. A demonstration project to prove the feasibility of borrow pit disposal was begun by the New York District (NYD). The project was not completed because of litigation, although research in other parts of the country showed that borrow pit disposal was technically feasible. Based on this information, the NYD is implementing an operational program for dredged material disposal into existing or new borrow pits. A Federal EIS is being prepared.

Recent progress is presented of ocean disposal activities and studies of alternatives to ocean disposal for contaminated dredged material from the Port of New York and New Jersey. The capping studies conducted in 1980-81 and subsequent monitoring have shown that ocean disposal of dredged material in the New York Bight can be managed effectively by pin-point disposal and capping when necessary to mitigate potential adverse environmental impacts. Disposal in subaqueous borrow pits with capping has been determined to be a technically feasible and environmentally suitable disposal alternative. Environmental clearances are currently being pursued to designate a borrow pit disposal site in New York Harbor, to be reserved only for dredged material not suitable for unrestricted ocean disposal. Siting studies are still being performed for locating a large containment island, and three potential sites have been identified in the Lower Bay of New York. Beach nourishment, upland disposal, use of dredged material as sanitary landfill cover, small containment areas and wetlands stabilization with dredged material are all possible in special cases on a project-by-project basis but not on a regional basis at this time. The results of these studies have demonstrated there is continued need for ocean disposal of the majority of dredged material from the Port, that ocean disposal can be managed effectively in an environmentally sound manner, and that there are a few potential disposal alternatives for the limited volumes of dredged material which are not suitable for unrestricted ocean disposal.

Determination of the fate of dredged material placed on the bottom of an ocean, lake, estuary, or river is an environmental concern that requires consideration and adequate prediction in the planning of a dredging project, since various natural processes can alter the initial configuration of the deposit and subject the surrounding bottom to some level of environmental impact. In the selection process for a disposal site, consideration must be given to the eventual disposition of dredged material in order that adequate determination of the site capacity can be made. The four primary environments that may contain subaqueous dredged material deposits are oceans, estuaries, rivers, and lakes, with various energy-related zones within each environmental system. Each zone has a unique set of physical factors and sedimentological properties that will determine the potential fate of a dredged material deposit. Methodologies for monitoring the actual physical changes that occur at a disposal site have been adequately documented at representative environments of deposition. As more knowledge is gathered, a better understanding of the interaction of the physical processes and the fate of subaqueous deposits of dredged material will be established.

The site selection process to implement a program for disposal of dredged material in existing or new subaqueous borrow pits in Lower New York Harbor requires preparation of a Federal Supplemental Environmental Impact Statement which will review and synthesize recent studies in this area. This Report utilizes an extensive fishery data base from recent ground trawl surveys (September 1984 to March 1986) in the Lower Bay Complex of the Hudson-Raritan Estuary to describe the fishery resources, it goes on to evaluate borrow pit sites in terms of this resource. The finfish community of the Lower Bay Complex, its species composition, abundance and biomass are described, including distributions within the area. Seasonal change in the community composition is described. Resident, transient, and migratory species are identified. Utilization of the area by juvenile stages of species of interest is also described. Two important shellfish, lobsters and blueclaw crabs, are described separately in terms of abundance and distribution. The data from the fishery analysis was used to develop criteria for identification within the Lower Bay Complex of areas of relatively low diversity and low use by the fish community. Criteria are given for the selection of five sites for potential dredged material disposal. These five sites are allocated priorities and then discussed in terms of recently proposed sites in the area.