Lower Duwamish Waterway, Seattle, WA: A Conceptual Cleanup Plan

摘要

Overview. The Lower Duwamish Waterway, a 5-mile-long, 441-acre site located in theindustrial core of downtown Seattle, Washington, was listed as a Superfund site in September2001 and as a Washington State Model Toxics Control Act (MTCA) site inFebruary 2002. Since that time, the risk assessments, sediment transport model, andRI/FS documents have been completed; and the draft Proposed Plan for the site is expectedin January of 2013. Human health risk drivers are total PCBs, arsenic, cPAHs, anddioxins/furans. The FS evaluated an array of remedial technologies including dredging,capping, enhanced natural recovery, carbon amendment, and monitored natural recoveryall of which are considered feasible to meet the four remedial action objectives (humanhealth seafood consumption, direct contact, benthic resources, wildlife seafood consumption).The estimated cleanup costs range from about $220 to $810 million, and constructiontimes span from 3 to 42 years depending in which remedial alternative isselected. Dredge volumes range from 300,000 to 3,900,000 cubic yards.Approach. The Lower Duwamish Work Group (LDWG), consisting of Port of Seattle,City of Seattle, King County, and the Boeing Company, identified key elements of thesite remedy that should be considered for the proposed plan. Features of the final FeasibilityStudy, ideas from the agencies, and stakeholder feedback were synthesized into aset of recommendations that is consistent with national guidance and (a) reduces humanhealth risks as early as possible, (b) reduces the time to achieve the RAOs, (c) minimizesshort-term impacts, and (d) ensures long-term effectiveness of the remedy.Results. This presentation will summarize the key elements put forth by LDWG that balanceshort-term risks with long-term benefits. Some of these elements include: dredgeintertidal areas to protect direct contact, dredge/cap areas with contaminants above actionlevels, apply ENR/MNR for moderate-to-low contaminated areas, add activated carbon tofurther reduce exposure of resident seafood species and gain additional risk reduction,and conduct a pre-design human use seafood consumption survey to assess human riskthrough social patterns. The key elements will be compared to EPA’s proposed plan forthe LDW.