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Your "toolkit" of cleanup ideas and conceptsYour tool kit for understanding the cleanup

Air deposition Contamination entering a site by being carried on the wind as dust.
AOPC Area of Potential Concern - where remediation efforts will occur within a Superfund cleanup.
ARAR “Legally applicable or relevant and appropriate standard, requirement, criteria or limitation” promulgated under federal or state environmental laws.
Background The contamination level at a site that cannot be removed due to its continuing existence in the environment. Waterways and sediments in urban areas have higher background contamination levels, called “urban background” than do undeveloped areas. Undeveloped areas have lower levels of contamination referred to as “natural background”.
“C” Alternatives

Alternatives within the Lower Duwamish Feasibility Study that focus on “Containment” of contamination through capping. “C” alternatives increase the seafood consumption risk, have longer construction periods and higher impacts for the community than do “C” alternatives.


Physically and/or chemically containing sediments in place. Achieved by placing clean sand, gravel or rock above contaminated sediments.

COC Chemical of Concern – the chemical contaminants that trigger a cleanup and are monitored to evaluate the effectiveness of a cleanup

Cleanup Screening Level (MTCA term; only minor adverse effects from sediment remain when achieved)

Dredging The physical removal of contaminated sediments from a waterway. Dredging projects increase and prolong the risk to human health from seafood consumption by stirring up contaminated sediments that are left behind during the dredging process and then consumed by fish.
EAA Early Action Area – specific sites within the Lower Duwamish Waterway cleanup area that the LDWG partners (King County, City of Seattle, Port of Seattle, The Boeing Company) agreed to clean up prior to the Superfund listing. These projects serve as the basis for every cleanup alternative proposed in the Feasibility Study.
ENR Enhanced Natural Recovery- encouraging natural processes that reduce health risks from contamination, typically by placing thin layers of clean materials on top of contaminated areas.
ICs Institutional Controls – nonengineered methods for reducing the risk from a Superfund site’s contamination, such as seafood consumption advisories or beach closures.
MNR Monitored Natural Recovery – tracking natural processes’ reduction of health risks from contamination
PRP Potentially Responsible Party – those entities the U.S. EPA believes to be responsible for the contamination at a Superfund site. There are more than 100 PRPs associated with the Lower Duwamish cleanup, including King County.
PRG Preliminary Remediation Goal – The level of chemicals of concern necessary to attain to achieve the cleanup’s risk reduction goals
“R” Alternatives Alternatives within the Lower Duwamish Feasibility Study that focus on “Removal” of contamination by dredging. “R” alternatives increase the seafood consumption risk, have longer construction periods and higher impacts for the community than do “C” alternatives.
RAL Remedial Action Level - The chemical of concern level triggering remediation at a Superfund site.
RAO Remedial Action Objectives – The cleanup’s risk reduction goals
ROD Record of Decision – The U.S. EPA’s formal announcement of its decision on how to clean up a Superfund site.
SMA Sediment Management Area – The area likely to be cleaned up during a Superfund.
SMS Sediment Management Standards – The cleanup’s criteria including Sediment Quality Standards and Cleanup Screening Levels

Sediment Quality Standards - more stringent than a CSL. All risk to biological resources or humans from sediment are removed at this level

SWAC Surface Weighted Average Concentration- Post-cleanup sediment concentrations, in this case describe the average PCB sediment concentration in the Lower Duwamish cleanup site.

Verification Monitoring

Lower Duwamish Waterway Group (LDWG) formed 2000
Superfund listing 2001
Initial assessments made 2000-2003
Remedial Investigation 2003-2010
Feasibility Study 2007-2012
EPA proposes cleanup plan 2013
EPA cleanup decision 2014
Pre-Design work by LDWG  2014-2019 
Negotiate Consent Decree 2018-2019
Cleanup design  2019-2023 
Cleanup activities begin (estimate) 2023
Full cleanup complete (estimate) 2030

The Lower Duwamish Sediment Superfund Cleanup goal is to reduce health risks from the waterway’s contaminated sediments for:

  1. People who eat seafood living in the Lower Duwamish (salmon are unaffected by the waterway’s sediment quality)
  2. People coming into contact with contaminated sediments on Lower Duwamish Waterway beaches
  3. Benthic organisms living in the waterway’s sediments
  4. Wildlife, including river otters

EPA will consider a range of evaluation criteria when making its decision about a final clean up alternative. Cost will be a consideration.

  1. Protection of human health and environment
  2. Compliance with state and federal requirements such as water quality standards
  3. Long-term effectiveness
  4. Short-term effectiveness
  5. Reduction of toxicity, mobility, or volume through treatment
  6. Implementability
  7. Cost
  8. State acceptance
  9. Community acceptance

All of the cleanup alternatives included in the Feasibility Study will meet the criteria to protect human health and the environment. However, they will differ in the amount of dredging to remove contaminants vs. capping, and the length of time.