International Dredging Review

International Dredging Review

In September the Port of Tacoma began dredging contaminated sediment in Blaire Waterway in preparation to expand Pier 4. The Port detected a marine biocide called tributyltin while completing a dredging inspection for the site evaluation to expand Pier 4 for larger ships. The Port of Tacoma has agreed to complete the cleanup of the sediments which the U.S. Environmental Protection Agency will oversee.

The Port of Tacoma will dredge an additional 500000 cubic yards of clean sediment to make the base of the pier deeper as part of the pier expansion.

In 2013 an investigation performed by the Port of Tacoma showed that the fill material used to create the bulkhead under Pier 4 was contaminated with TBT.

Developed to be toxic to aquatic life TBT is a marine biocide commonly added to ship paint to prevent mollusks from sticking onto vessels and other objects that contain the chemical. EPA canceled all TBT antifouling paint product registrations in December of 2005.

The Port of Tacoma removed the Pier 4 deck and piling between May and August and plans to dredge approximately 40000 cubic yards of contaminated sediments. The contaminated sediments will be dewatered and trucked to a waste disposal facility. The Superfund phase of the work is expected to be completed by April of 2016 with an overall cost of $19.3 million.

The Port of Tacoma consulted with the Washington Department of Fish and Wildlife and came to the conclusion that dredging would be least harmful to out-migrating fish if dredging started after the beginning of August.

“To minimize the potential for impacts to salmon while dredging the contaminated sediments we worked with NMFS and WDFW to begin dredging in August to reduce the chances that a work extension would be needed to complete the cleanup when smaller out migrating juvenile chinook salmon may be present” said Scott Hooton Port of Tacoma environmental project manager “We have also made detailed guidelines for how to operate the clamshell bucket to accurately dredge the required depth and area as well as making sure the lid is fully secure before lifting through the water to minimize sediment loss.”