Alameda Point’s Seaplane Lagoon Dredging Completed

Northwest Seaplane Lagoon dredge sediment drying area

Sediment sits here to dry out until later in the year before testing and removal.

 Credit Richard Bangert 

Dredging through the night at Alameda Point
Seaplane Lagoon dredging at sundown 
Credit Richard Bangert

The dredging project at Alameda Point’s Seaplane Lagoon reached a major milestone in February 2012. The dredging of the northwest corner has been completed, and the sediment will be allowed to dry out before being tested and hauled away in the fall.

The two-part dredging project that started in early 2011 at the northeast corner was preceded by the removal and replacement of thousands of feet of radium-contaminated storm sewer lines leading to the lagoon.

The dredging of the northwest corner went much quicker than at the northeast corner. This is because the three-acre northwest work area is half the size of the northeast area, and also because the new contractor for the project used a larger dredging rig.  The original dredging contractor did not have their contract renewed after failing to complete the entire dredging part of the project by the arrival of the least terns last April. The April deadline was because the terns feed in the lagoon during nesting season, and dredging is considered a disturbance of an endangered species.

Out of the 75,628 cubic yards of sediment removed from the lagoon at the northeast area, 1,719 cubic yards, or 2%, were hauled to a hazardous waste facility. Eleven cubic yards of that amount were hauled to a low-level radiological waste disposal site. The rest of the sediment is deemed safe enough to reuse as fill material to cover the old landfill at the southwest corner of Alameda Point. It has been hauled to a temporary holding area on the Wildlife Refuge.

The main reason that most of the sediment from the northeast area went from toxic to safe is because the contaminated sediment went down three feet into the floor of the lagoon, but the dredging went to five feet, which essentially diluted everything.  Also, the main contaminants, which included PCBs, cadmium, and pesticides, were not uniformly distributed in the sediment.

At the March Restoration Advisory Board meeting, the Navy said that the northeast drying area that extends westward from the Naval Air Museum is now cleaned up, and that the fence can be removed for that area.

By the time everything is hauled away and the work area demobilized, the entire dredging project will cost the Navy $46 million.

Read more about Alameda Point cleanup and open space issues on the Alameda Point Environmental Report.

Source:  http://alameda.patch.com