A.60 Port of Tacoma Piers 24 and 25, WA

A.60.1 Summary

Environment:	Tidal flat
Scale:	Full
Contaminants of Concern:	Metals (zinc, copper, mercury), phenanthrene, dibenz(a,h)anthracene, PCBs, and hexchlorobutadine (HCBD)
Final Remedy:	Debris removal, excavation, and cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment.

A.60.2 Site Description

The Port of Tacoma’s Piers 24 and 25 are located in Tacoma, Washington at the mouth of the Hylebos Waterway, which is part of the Commencement Bay/Tideflats Superfund Site. Chemicals were primarily introduced to the site by direct and indirect discharges of contaminated wastewater from the now-demolished Tacoma/Asarco Smelter. Cleanup activities began in the Hylebos Waterway in 2002 and a 2005 Consent Decree required capping under Piers 24 and 25.

A.60.3 Remedial Approach

Final selected remedy: Debris removal, excavation, and capping

The Piers 24 & 25 Embankment Capping Area includes intertidal and subtidal areas along an embankment approximately 1,200 ft long and including the wharf covered slopes beneath Piers 24 and 25. Capping began in October 2007 and was finished in 2009.

During the construction of the caps and the armor stone on the wharf covered slopes beneath Piers 24 and 25, a few practical methods of reducing construction impact on water quality were effectively implemented. Debris removal, PCB hot spot excavation, and metallic debris pile excavations were conducted during low tide periods as much as practical. Shotcrete capping materials were placed when possible during low tide and using quick-set formulation. Other capping materials were also placed in the dry as possible and placed using low-disturbance techniques below the waterline when necessary. The quantity of capping materials used to construct a “toe berm” at the base of the slope was significantly higher than anticipated due to small design tolerances, difficulty of placement in relatively soft sediments, and difficulty with controlling settlement and downslope movement.

A.60.4 Monitoring

Pre- and post-construction samples showed no exceedances of Commencement Bay sediment quality objectives (SQOs) and visual inspections confirmed that the caps remain intact.

This project had issues with community acceptance. A technically feasible option was proposed previously but was rejected by a community who felt their input was not sought/incorporated thoroughly enough. They then re-worked their entire plan and added significant stakeholderAffected tribes, community members, members of environmental and community advocacy groups, and local governments. and community input/review to come up with a new accepted feasible option. This held up remediationThe act or process of abating, cleaning up, containing, or removing a substance (usually hazardous or infectious) from an environment. by several years.

 

Publication Date: August 2014