RIASSUNTO
ABSTRACT
This paper summarizes the data obtained from site surveying and sediment sampling of dredge spoil disposal mounds at the Central Long Island Sound site. Emphasis is placed on the geotechnical and geological features of the mound natural seabed. Since some of the spoil is contaminated, cappings of clean spoil have been used to isolate the spoil mounds from fauna and flora in the water column. Because of the contaminated spoil, improvements in the disposal techniques are needed and methodologies must be developed for evaluating short-term and long-term stability of these shallow ocean deposits whi.ch are subjected to loadings from waves, spoil disposal arid capping operations.
INTRODUCTION
Most navigable rivers require periodic, dredging. The coasts of Connecticut and long Island are too densely populated for up plan disposal of the dredge spoil to be an economical solution and shallow ocean disposal has became an accepted practice. Before there was a general awareness of the environmental problems that dredge disposal may entail, disposal sites proliferated in Long Island Sound. In addition the industrial concentration around the Sound has lead to some pollution of bottom sediments in the rivers and harbors (N.E. River Basin Commission, 1980). Although most sources of pollution have been eliminated dredge spoil from certain areas still contain undesirable levels of contaminants.
A recent solution to controlling the spoil disposal problem has been to limit shallow ocean disposal in Long Island Sound (LIS) to four sites approved by the U.S. Army Corps of Engineers (Morton and Karps, 1982; U.S. Army Corps, 1983). While there have been tens of disposal sites created in LIS during the last 50' years, the Corps has opted to restrict disposal to these four sites for purposes of monitoring long-term environmental impact with their Dredge Area Maintenance and Observation System (DAMOS) program initiated in 1975 plus some other recent programs. As a result of the DAMOS program it is possible to study and assess the impact of spoil disposal from dredge site to disposal site including both environmental and economic issues. One of the important issues is the potential affects of dredge spoil disposal on the fish industry. Shallow ocean disposal eliminates the problem of justifying upland/wetland disposal for each dredging project but requires that costlier clamshell dredging and barge transport be used. The effectiveness of clamshell dredging is not well defined since it re-suspends particles during dredging. In addition, there is concern that benthic fauna and flora may react adversely to the contaminated spoil mounds and the disposal plume.
As recently as 1979 (Morton, 1980) a capping of clean spoil has been used to isolate contaminated spoil rounds. This process consists of taking clean spoil from a nearby project and spreading it over a contaminated mound to achieve isolation of the polluted spoil.