Environmental cleanup of the Seaplane Lagoon has centered on two areas where storm sewers drain into the lagoon. It was commonplace to discharge all sorts of chemicals down storm sewer lines prior to the passage of the federal Clean Water Act in the early 1970s. Contaminants such as PCBs, cadmium, lead, pesticides, and radium have been found in the sediment around the sewer discharge points.
Prior to dredging, sewer lines leading to the northeast and northwest corners were either replaced or flushed out. An underwater debris pile of metal and wood was also removed at the northeast corner before dredging.
The Northeast Corner
Setup for the 6.5-acre northeast dredging area began in late 2010, and dredging was completed in April of 2011. The total amount of sediment removed was 75,628 cubic yards. Even though the contamination depth was three feet, the dredging went to five feet.
Only 1,719 cubic yards of sediment were transported to hazardous waste disposal sites, of which 11 cubic yards went to a low-level radiological waste disposal site because of the radium-226. The rest of the sediment was determined to be safe enough for reuse, in large part because the contaminants were diluted by the over-dredging of clean sediment. The clean sediment has been stockpiled on the western end of the Wildlife Refuge for future use in capping the landfill disposal sites 1 and 2.
All of the drying pad materials for the northeast corner have been removed, which will allow for the fence to be moved.
The Northwest Corner
Setup for the 3.3-acre northwest corner began in October of 2011 with the construction of a concrete, waterproof drying pad. Prior to dredging, a sunken barge was demolished and removed. The barge pieces were scanned for radiation, but none was found. The 66 tons of scrap iron was sent to a recycling facility.
Dredging started on January 16 and ended on February 22. The dredging at the NW corner went much faster than the early dredging, partly because of the smaller area, and partly because of heftier dredging equipment.
Unlike the NE corner, however, the sediment here is expected to contain higher levels of radium-226 because the sewer line leading here was highly contaminated. As was the case at the NE corner, this sediment will have to dry out before being tested and disposed of. The project should be completed and everything removed by December.
The price tag for all of the Seaplane Lagoon dredging and hauling away sediment, when completed: $46 million.