Looking at the chart this area is between the shoal coming north west from Eatons Neck and Cable and Anchor Reef. The shoal is 16' and the reef is 26' but the area between is down as far as 125' so the current is ripping through there. Based on this new location I would expect the bottom in that area to be hard and any dredge spoils dumped on top would have been carried away over time. These things may not be buried at all.
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I could not see any shoreline in either of those to give a better hint of the location. From your second map site C is on a direct line from Eatons Neck to Norwalk not Bridgeport.
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The only mention of the dump sites in this area follows. This came from the Army Corp of Engineers. Might be a good idea to contact them to see if you can get more details on the site location and what else may have been dumped there. I would give special attention to finding out what types of chemical hazards may be there.
On September 1, 1981, the Applicants again requested that their permits be modified, this time to allow dumping further west in the Sound. The purpose of the modification was to gain access to a site which would entail lower transportation costs than the CLIS site. The Applicants, still acting collectively, stated that the new modification might be "the difference between the entire project going forward, being severely cut back, or indefinitely postponed." However, of the 19 historically used sites scattered throughout the Long Island Sound, 16 had been closed for environmental reasons, leaving the western Sound without a dumpsite. In order to fulfill the modification request, the Corps was required to designate a new dumpsite. The Applicants suggested that there were several potential sites which could be used, including "the triangle site bordered by the old [closed] Stamford, Norwalk and Eatons Neck Dump Sites." The Corps adopted this suggestion, proposing to designate this site located off the shores of Huntington, New York as Western Long Island Sound III ("WLIS III"). The Corps also proposed to utilize the newly designated site as the repository for spoils from additional federal dredging projects. In its public notice announcing the proposal to designate WLIS III, the Corps listed two "[p]lanned Federal projects which could be served" by the new site. The Corps intended to dredge 530,000 cys of waste from Flushing Bay, New York and 30,000 cys from Mianus River, Connecticut. With the addition of the 86,000 cys from Mamaroneck Harbor, the new site from its inception was intended to be the repository of at least 646,000 cys of dredged waste material--well in excess of the 560,000 cys projected for WLIS III by the Corps in its public notice.
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I keep looking at the first video and it looks like they are a lot closer to land then I would expect to see from site C. If they were worried about people recovering them what they told the press about the location may have been disinformation. They may have dumped them at sites A or D.