Proposed Plan
Lower Duwamish Waterway
Superfund Site
s>EPA
United States
Environmental Protection Agency
Region 10
February 28, 2013
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Opportunities to Comment on this Plan
This Proposed Plan includes a summary of the cleanup alternatives evaluated and a description of the U.S.
Environmental Protection Agency's (EPA's) Preferred Alternative for cleanup of the Lower Duwamish
Waterway Superfund Site. EPA is seeking comments on the Proposed Plan, including the Preferred
Alternative, other alternative remedies considered, and the supporting analysis and information in the
Administrative Record. Because of the high level of public interest in this Site, and because EPA has already
received a request for a 45-day extension to the 60-day comment period initially considered, EPA has
provided for a 105-day public comment period instead of the usual 30 days. EPA will accept comments from
February 28 until June 13, 2013.
This Plan summarizes information that can be found in greater detail in the Remedial Investigation and
Feasibility Study reports, other key documents identified in this Proposed Plan, and other documents
maintained at the Information Repositories for the Site (see below for locations).
Where to Review the Proposed Plan and Administrative Record
The Administrative Record, which contains the Proposed Plan and other documents that form the basis for
the proposed Preferred Alternative, is available for public review at these Information Repositories:
EPA Region 10 Superfund Records Center South Park Public Library
Opportunities to Review and Comment on this Plan
Written comments on this Proposed Plan and other documents listed below can be submitted at any time
during the public comment period in any of the following ways:
• Post to the comments website: www.resolv.org/site-ldpc
• E-mail: ldpc@resolv.org
• Fax: 206-450-5999
• Mail: Allison Hiltner, EPA Region 10, 1200 Sixth Avenue, Suite 900, MS ECL-111, Seattle WA 98101
Public meetings will be offered during the public comment period. EPA will take oral as well as written
comments at those meetings. Meeting information will be published in the Seattle Times and other
publications and locations, as well as on EPA's website: www.epa.gov/regionlO/duwamish.html
EPA will respond to comments received during the public comment period in a Responsiveness Summary
which will be part of EPA's Record of Decision (ROD) that selects the final remedy.
Two important documents are appended to the Proposed Plan for the convenience of reviewers. Although
these documents are not part of the Proposed Plan, they will be carefully considered in the development of
the ROD as well as its implementation. The two appendices are: A) Ecology's Lower Duwamish Waterway
Source Control Strategy, and B) EPA's Environmental Justice Analysis for the Lower Duwamish Waterway
Cleanup. Ecology is concurrently seeking comments on its Source Control Strategy, and EPA is concurrently
seeking comments on its Environmental Justice Analysis. Comment responses for those two documents will
be separate from comment responses for this Proposed Plan.
1200 Sixth Avenue, Suite 900, MS ECL-076
Seattle, WA 98101
206-553-4494
8604 Eighth Avenue South
Seattle, WA 98108
206-615-1688
Other Documents Available for Review and Comment
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Executive Summary
Over 100 years of industrial and urban use has polluted the sediments, water, and marine life in the Lower
Duwamish Waterway (LDW). This Proposed Plan presents the U. S. Environmental Protection Agency's
(EPA's) Preferred Alternative to clean up contamination in the in-waterway portion of the LDW Superfund
Site. There are three components to the strategy proposed by EPA and the Washington Department of
Ecology (Ecology) for cleaning up the LDW: 1) early identification and cleanup of the most contaminated
areas in the waterway, referred to as Early Action Areas (EAAs); 2) controlling sources of contamination to
the waterway; and 3) cleanup of the remaining contamination in the waterway—addressed in this Proposed
Plan—including long-term monitoring to measure the success of the remedy in achieving cleanup goals.
Cleanups have been completed at three EAAs, and are underway at two more EAAs. Ecology is the lead
agency for the second component of the strategy, source control. Ecology and other agencies have made
substantial progress towards finding, investigating, and controlling historical and ongoing sources to the
LDW, though more work remains. Appendix A provides Ecology's strategy for its continuing efforts to
identify and address sources of contamination to the waterway.
The proposed cleanup in this plan addresses the third component of this strategy, cleanup of the in-waterway
portion of the Site. It is based on four goals, which EPA calls Remedial Action Objectives (RAOs):
RAO 1: Reduce to protective levels the human health risks associated with consumption of contaminated
Lower Duwamish Waterway resident fish and shellfish by adults and children with the highest potential
exposure.
RAO 2: Reduce to protective levels the human health risks from direct contact (skin contact and incidental
ingestion) to contaminated sediments during netfishing, clamming, and beach play.
RAO 3: Reduce to protective levels the risks to benthic invertebrates from exposure to contaminated
sediments.
RAO 4: Reduce to protective levels the risks to crabs, fish, birds, and mammals from exposure to
contaminated sediment, surface water, and prey.
The cleanup alternatives in the Proposed Plan list actions that must be taken if specific numerical criteria are
exceeded. The two primary criteria used to determine if cleanup is needed are:
1) Long-term goals, which EPA calls Preliminary Remediation Goals (PRGs); and
2) Remedial Action Levels, (RALs), which trigger cleanup action in certain areas, and allow for
Monitored Natural Recovery in other areas where contamination levels are low.
Active cleanup will include a combination of the following:
• Dredging contaminated sediments;
• Capping contaminated sediments with clean material; or
• Enhanced Natural Recovery, which means adding about six to nine inches of clean material (such as
sand) to areas with moderate amounts of contamination, with possible amendment with activated
carbon or other substances that make contaminants less harmful.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
The method of active cleanup will depend on several different things, such as:
• The type and amount of contamination;
• The depth of the contamination;
• The likelihood that people will come into contact with the contamination through activities like
clamming or playing on the beach;
• The likelihood of fish, shellfish, or other marine creatures coming into contact with the
contamination;
• The likelihood that "vessel scour" (a ship or other marine vessel churning up the sediments) or other
activities such as building docks or piers will bring contamination up to the surface or suspend it in
the water;
• The need to maintain water depths and habitat so that people and marine creatures can continue to
use the waterway; and
• The likelihood of natural processes depositing cleaner sediments from upriver in a particular area.
Areas with low levels of contamination that are not specified for active cleanup will still be watched. They
are called Monitored Natural Recovery areas. To make sure the waterway recovers in these areas, EPA will
sample throughout the natural recovery period to make sure that clean material from upstream builds a clean
layer above the current waterway bottom. If sampling results show the waterway isn't clean enough
considering the criteria established in this plan, EPA will determine whether additional cleanup is necessary.
EPA considered many alternatives and is proposing the Preferred Alternative described in this Proposed Plan
because we believe it provides the best balance between minimizing the time it takes to reduce contaminant
concentrations in the waterway, and providing for a thorough and protective cleanup that minimizes the risk
of future releases of buried contamination. The cleanup proposed in this plan, in addition to cleaning up the
EAAs and controlling sources of contamination to the waterway, is estimated to reduce risks from people
eating contaminated fish and shellfish by 90% or more.
EPA estimates that the proposed cleanup will take about 7 years to implement, with an additional 10 years to
reduce contaminant concentrations to their lowest predicted concentrations through natural recovery. The
proposed cleanup plan addresses 156 acres of contaminated sediments through dredging, capping, or
Enhanced Natural Recovery, removing an estimated 790,000 cubic yards of contaminated sediments from the
waterway. Contaminant concentrations in the rest of the waterway will be reduced through cleanups at the
EAAs (29 acres) or Monitored Natural Recovery areas (256 acres). The estimated cost of the proposed
cleanup is $305 million.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Contents
Opportunities to Comment on this Plan i
Executive Summary iii
Acronyms and Abbreviations viii
1 Introduction l
2 Site Background 5
2.1 Cleanup Activities Planned and Completed to Date 7
2.2 Source Control Investigations and Actions Completed to Date 8
2.3 Public Involvement 11
2.4 Involvement by Federally Recognized Tribes 11
2.5 Environmental Justice Analysis 11
3 Lower Duwamish Waterway Setting 13
3.1 Land Use 13
3.2 Waterway Use 14
3.3 Ecological Communities in the LDW 14
3.4 Sediment Transport and Deposition 16
3.5 Extent of Contamination 19
3.6 Background and Upstream COC Concentrations 25
4 Summary of Site Risks 29
4.1 Human Health Risks 29
4.2 Ecological Risks 37
4.3 Basis for Action 38
5 Scope and Role of the Response Action 41
5.1 Component 1: Early Identification and Cleanup of EAAs 41
5.2 Component 2: Controlling Sources of Contamination 41
5.3 Component 3: In-Waterway Cleanup 42
6 Remedial Action Objectives 43
7 Preliminary Remediation Goals 45
7.1 Sediment PRGs 45
7.2 Fish and Shellfish Tissue PRGs 48
7.3 Surface Water PRGs 49
8 Development of Remedial Alternatives 51
8.1 Framework for Developing Remedial Alternatives 51
8.2 Summary of Remedial Alternatives 53
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Proposed Plan — Lower Duwamish Waterway Superfund Site
9 Evaluation of Alternatives 73
9.1 Threshold Criteria 74
9.2 Balancing Criteria 82
9.3 Modifying Criteria 86
9.4 Summary of CERCLA Evaluation 87
10 EPA's Preferred Alternative 89
10.1 Description of the Preferred Alternative 89
10.2 Implementation of the Preferred Alternative 93
10.3 Rationale for Identification of 5C Plus as the Preferred Alternative 94
10.4 Preferred Alternative Summary 96
11 Key Terms 105
12 Key Documents 109
List of Tables
Table 1. Statistical Summaries for Human Health COCs in Sediment 20
Table 2. Summary of Selected Human Health COCs in Fish and Shellfish Tissue3 24
Table 3. Summary of PCB, Arsenic, cPAH, and Dioxin/Furan Data for Natural Background
Concentrations in Sediment 26
Table 4. Estimates of Sediment and Suspended Sediment COC Concentrations of PCBs,
Arsenic, cPAHs, and Dioxins/Furans from Upstream of the LDW Study Area 27
Table 5. Summary of PCB, Arsenic, cPAH, and Dioxin/Furan Data for Natural Background
Concentrations in Fish and Shellfish Tissue 28
Table 6. Cancer and Non-Cancer Risk Estimates for Human Health Scenarios 32
Table 7. Surface Sediment Contaminant Concentrations and Comparison to SMS Numerical
Standards 38
Table 8. Sediment PRGs for PCBs, Arsenic, cPAHs, and Dioxins/Furans for Human Health and
Ecological COCs 46
Table 9. Sediment PRGs for Ecological (Benthic Invertebrate) COCs 47
Table 10. LDW Resident Fish and Shellfish Tissue PRGs 49
Table 11. Criteria for Assigning Recovery Categories 52
Table 12. Remedial Alternatives and Associated Remedial Technologies, Remedial Action
Levels, and Actively Remediated Acres 60
Table 13. Remedial Alternative Areas, Volumes, and Costs 61
Table 14. Alternative 5C Plus Ecological Risk Reduction (Benthic Protection) RALs 71
Table 15. Key ARARs for the LDW 80
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Proposed Plan — Lower Duwamish Waterway Superfund Site
List of Figures
Figure 1. Lower Duwamish Waterway and Early Action Areas 4
Figure 2. LDW Parks, Beach Play, and Potential Clamming Areas 15
Figure 3. Potential Scour Areas and Estimated Net Sedimentation Rates 18
Figure 4. PCB Distribution in Surface Sediment 21
Figure 5. SMS Status in Surface Sediment 22
Figure 6. Conceptual Model for Baseline Human Health Risk Assessment 30
Figure 7. Baseline Excess Cancer Risk and Non-Cancer Hazard Quotients for Consumption
of Various Seafood Species as a Function of the Number of Meals Consumed
per Month 34
Figure 8. Baseline Non-cancer Hazard Quotients and Excess Cancer Risk for the Seafood
Consumption RME Scenarios 35
Figure 9. Baseline Excess Cancer Risk for the Direct Sediment Contact RME Scenarios 36
Figure 10. Conceptual Site Model for LDW Fish and the Benthic Invertebrate Community 40
Figure 11. Conceptual Site Model for Wildlife 40
Figure 12. Recovery Categories 54
Figure 13. Areas Addressed by LDW Cleanup Alternatives 55
Figure 14. Summary of Alternatives 63
Figure 15. Time to Achieve Risk Benchmarks for All Alternatives 65
Figure 16. Excess Cancer Risks and Non-cancer HQs for Seafood Consumption Calculated
Using Tissue PRGs 76
Figure 17. Comparison of Total PCB Excess Cancer Risks and Non-cancer HQs for Seafood
Consumption Calculated using LDW Baseline, Model-predicted,
and PRG Concentrations 77
Figure 18. Preferred Alternative 97
Figure 19. Intertidal Areas - Remedial Technology Applications 99
Figure 20. Subtidal Areas - Remedial Technology Application 101
Figure 21. Intertidal Areas - Remedial Action Levels Application 103
Figure 22. Subtidal Areas - Remedial Action Levels Application 104
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Acronyms and Abbreviations
(ig/kg micrograms per kilogram
ARAR applicable or relevant and appropriate requirement
AWQC Ambient Water Quality Criteria
BEHP bis(2-ethylhexyl)phthalate
bg natural background
BCM bed composition model
C combined technology
CAD contained aquatic disposal
CERCLA Comprehensive Environmental Response, Compensation, and Liability
Act
CFR Code of Federal Regulations
COC contaminant of concern
cPAH carcinogenic polycyclic aromatic hydrocarbon
CSL cleanup screening level
CSO combined sewer overflow
cy cubic yard
DMMP Dredged Material Management Program
dw dry weight
EAA Early Action Area
Ecology Washington Department of Ecology
EJ environmental justice
ENR enhanced natural recovery
EPA U.S. Environmental Protection Agency
ESA Endangered Species Act
FS feasibility study
HHRA human health risk assessment
HP AH high molecular weight polycyclic aromatic hydrocarbon
HWTR Hazardous Waste Toxicity Reduction
FS feasibility study
Vlll
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Proposed Plan — Lower Duwamish Waterway Superfund Site
FEMA
Federal Emergency Management Act
KCC
King County Code
LDW
Lower Duwamish Waterway
LPAH
low molecular weight polycyclic aromatic hydrocarbon
mg/kg
milligrams per kilogram
MCL
maximum contaminant level
MCLG
maximum contaminant level goal
MLLW
mean lower low water
MHHW
mean higher high water
MNR
monitored natural recovery
MTCA
Model Toxics Control Act
na; n/a
not applicable
NCP
National Oil and Hazardous Substances Pollution Contingency Plan
nc
cannot be calculated
nd
not detected
NEPA
National Environmental Policy Act
ng/kg
nanograms per kilogram
ng/L
nanograms per liter
NO A A
National Oceanic and Atmospheric Administration
OC
organic carbon
OM&M
operation, maintenance, and monitoring
PCB
polychlorinated biphenyl
PRG
preliminary remediation goal
R
removal emphasis
RAL
remedial action level
RAO
remedial action objective
RBTC
risk-based threshold concentration
RCW
Revised Code ofWashington
RI
remedial investigation
RME
reasonable maximum exposure
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Proposed Plan — Lower Duwamish Waterway Superfund Site
RM
river mile
ROD
Record of Decision
R-T
removal with physical treatment
SCWG
Source Control Work Group
SD
storm drain
SEPA
State Environmental Policy Act
SMS
Sediment Management Standards
SQS
sediment quality standard
STM
sediment transport model
SVOC
semivolatile organic compound
SWAC
spatially-weighted average concentration
TBD
to be determined
TEQ
toxic equivalent
TOC
total organic carbon
U.S.C.
United States Code
VOC
volatile organic compound
WAC
Washington Administrative Code
WDOH
Washington Department of Health
WW
wet weight
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Proposed Plan — Lower Duwamish Waterway Superfund Site
1 Introduction
This Proposed Plan (Plan) presents the U. S. Environmental Protection Agency's (EPA's) Preferred
Alternative to clean up contamination in the in-waterway portion of the Lower Duwamish Waterway
(LDW) Superfund Site (Site). This Plan describes contamination present in the LDW and the associated
risks to human health and the environment, the cleanup alternatives considered, and EPA's Preferred
Alternative to address these risks. This Plan is issued by EPA, as the lead agency for the in-waterway
portion of the Site, in accordance with the public participation requirements of the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA, 42 U.S.C. 9601 et seq. as
amended) Section 117(a) and under 40 CFR Section 300.430(f)(2) of the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP).
The LDW Site, located south of downtown Seattle, Washington, extends over the northern five miles of
the Duwamish River to the southern tip of Harbor Island (Figure 1), and includes the waterway as well as
the upland sources of contamination. Industrial discharges, storm drains (SDs), and combined sewer
overflows (CSOs) have polluted LDW surface water and sediments over the past 100 years. Numerous
hazardous substances were found in sediments at concentrations that pose a risk to humans through
consumption of seafood, and through direct exposure when playing on the beach, clamming, or
netfishing. Sediment contamination also poses an ecological risk to bottom-dwelling organisms and to
mammals such as river otters. Polychlorinated biphenyls (PCBs), arsenic, carcinogenic polycyclic
aromatic hydrocarbons (cPAHs), and dioxins/furans are the four contaminants of concern (COCs) that
account for most of the human health risk. In addition, 41 COCs have been found to pose risks to bottom-
dwelling organisms in the LDW.
The overall strategy for addressing contamination and the associated risks in the LDW and surrounding
watershed includes three components: 1) early identification and cleanup of the most contaminated areas
in the waterway, referred to as Early Action Areas (EAAs); 2) controlling sources of contamination to the
waterway; and 3) cleanup of the remaining contamination in the waterway, including long-term
monitoring to assess the success of the remedy in achieving cleanup goals.
Progress on component 1, cleanup of the EAAs, is described in Section 2. For component 2, source
control, Ecology is the lead agency with EPA as a support agency. Ecology's source control activities are
described in their Lower Duwamish Waterway Source Control Strategy (Source Control Strategy), which
is attached as Appendix A. For component 3, cleanup of the in-waterway portion of the Site, EPA is the
lead agency and Ecology is the support agency.
This Proposed Plan describes and invites comments on EPA's Preferred Alternative for cleanup of the in-
waterway portion of the LDW. The Preferred Alternative is intended to be the final remedy for the in-
waterway portion of the Site, to be implemented after cleanup in the EAAs has been completed, source
control sufficient to minimize recontamination has been implemented, additional sampling and analysis
has been conducted, and design of the remedy has been completed.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
The Preferred Alternative, which addresses approximately 412 acres, includes the following elements:
• A total of 156 acres of active cleanup, consisting of:
84 acres of dredging or partial dredging and capping (an anticipated total volume of 790,000
cubic yards would be dredged and disposed in an upland landfill);
- 24 acres of capping, with possible amendment with activated carbon or other contaminant-
sequestering agents; and
- 48 acres of Enhanced Natural Recovery (ENR - placing 6 to 9 inches of clean material over
contaminated sediments) with possible amendment with activated carbon or other contaminant-
sequestering agents, if these amendments are shown to be effective in pilot tests.
• Further reduction of contaminant concentrations over time in the remaining 256 acres through
Monitored Natural Recovery (MNR - relying on natural processes such as burial of contaminated
sediments by cleaner sediments from upstream). Long-term monitoring data will determine whether
additional cleanup actions will be necessary in MNR areas.
• Institutional controls (ICs) and LDW-wide monitoring to enhance and measure protectiveness, and to
protect the integrity of remedial action elements such as capping and ENR, while minimizing reliance
on seafood consumption-related ICs to the extent practicable.
The Preferred Alternative assumes completion of an additional 29 acres of cleanup in Early Action Areas
(see Sections 2 and 5 for further discussion of the EAAs).
Implementation of the Preferred Alternative, or another cleanup alternative described in this Plan, is
considered necessary to protect human health and the environment from actual or threatened releases of
hazardous substances. EPA is seeking comments on this Proposed Plan, including the Preferred
Alternative, other alternatives considered, and the supporting analysis and information located in the
Information Repositories (see page i), including the Remedial Investigation and Feasibility Study reports
(RI Report and FS Report) and other key documents listed on page i. Public comments will be used by
EPA, in consultation with Ecology and the Muckleshoot and Suquamish Indian Tribes, to select the final
remedy in its Record of Decision (ROD). EPA may modify the Preferred Alternative or select another
cleanup alternative presented in this Plan based on new information or public comments. Therefore, the
public is encouraged to review and comment on all the alternatives.
EPA anticipates issuing the ROD in 2014. The ROD will include a Responsiveness Summary
summarizing and responding to public comments on the Proposed Plan. Once the ROD is issued, a
detailed design of the cleanup, called remedial design, will follow, followed by implementation of the
remedy, then long-term monitoring. Remedial design sampling will be conducted after the early actions
are completed in 2015. Results from remedial design sampling will be used to determine the final areas
and volumes to be remediated and the remediation technologies to be applied and may be used by
Ecology to assist in their source control efforts. Decision criteria for modifying the cleanup footprint
based on remedial design data are included in Section 10.2.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
The Preferred Alternative is estimated to take 7 years to construct. The lowest contaminant concentrations
in fish and shellfish tissue are predicted by modeling to be achieved in 17 years following the start of
construction.
Total estimated net present value costs are $305 million, of which capital costs are $258 million, and
operation, maintenance, and monitoring (OM&M) costs are approximately $47 million.
In addition to Appendix A, Ecology's Source Control Strategy, this Proposed Plan presents EPA's
Environmental Justice Analysis for the Lower Duwamish Waterway Cleanup (EJ Analysis) as Appendix
B. These documents are not part of the Proposed Plan, but they will be carefully considered in the
development of the ROD as well as its implementation.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
ty.af as
Washington
Oregon
Elliott
Bay
Seattle
Puget
Sound
¦¦1
LDW Study Area
Early Action Area (EAA)
== River Mile
0.5 1
Miles
0.5 1
~ Kilometers
Figure 1. Lower Duwamish Waterway and Early Action Areas
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Proposed Plan — Lower Duwamish Waterway Superfund Site
2 Site Background
This section provides an overview of LDW topography and history, along with brief descriptions of
contaminant sources, waterway use, and risks posed by contaminants.
LDW Topography and History
The Lower Duwamish Waterway (LDW) and adjacent upland areas have served as Seattle's major
industrial corridor since the LDW was created by widening and straightening much of the Duwamish River
in the early twentieth century. The Duwamish River flows north through Tukwila and Seattle, splitting at
the southern end of Harbor Island to form the East and West Waterways, prior to discharging into Elliott
Bay in Seattle, Washington. The in-waterway portion of the LDW Site evaluated for remedial action in this
Proposed Plan extends for approximately 5 miles from the area around the Norfolk CSO (Norfolk EAA, at
the southern end of the Site) at RM 5 to the southern tip of Harbor Island at river mile (RM) 0 (Figure 1). In
total, the LDW includes approximately 441 acres of intertidal and subtidal habitats. The average width of
the LDW is 440 feet.
Most of the upland areas adjacent to the LDW have been heavily industrialized since the early 1900s.
Industrial uses include shipyard operations; manufacturing (airplane, cement, and chemical, e.g., paint,
glue, resin, and wood preservatives); cargo storage and transport; metal manufacturing and recycling;
petroleum storage; and the disposal of waste in landfills. Some of the wastes generated or disposed during
these operations may have been discharged into or otherwise come to be located in the LDW, and may have
contributed to the contamination of the LDW. Pathways for contaminants to enter the LDW can be direct
(e.g., a stormwater discharge through a pipe into the LDW) or indirect (e.g., atmospheric deposition of
contaminants within the watershed).
Contaminant Sources and Waterway Use
Within the LDW, sources of contaminants in LDW surface water and sediments include stormwater
carrying the contaminants to the LDW via creeks, ditches, SDs, and CSOs; upland sites with contaminants
reaching the LDW via groundwater, surface water, or erosion of contaminated soils; and atmospheric
deposition to the LDW. Surface water and stormwater are major pathways for contaminants to enter the
LDW. There are 208 pipes, creeks, and streams directly discharging into the LDW. Of these, 203 are public
or private outfalls and five are creeks or streams. Twelve of the outfalls are CSOs, which discharge
wastewater (residential, commercial, and industrial) and stormwater runoff. The potential source area
discharging to the LDW encompasses a total area of 20,400 acres or approximately 32 square miles and
includes: 1) the combined (sanitary and stormwater) sewer system, 2) the sanitary sewer service area, and
3) the separated stormwater drainage basins.
The CSO discharges typically occur during large storm events when the capacity of the combined sewer is
exceeded and not all flow can be conveyed to a treatment plant. Non-CSO stormwater enters the waterway
via storm drains and pipes, ditches, and creeks, or directly from properties adjacent to the waterway.
Stormwater can carry contaminants when rain has come into contact with contaminants that have
accumulated in or on soils and surfaces and subsequently drains into the stormwater system. The
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contaminants that collect in storm drains/pipes, ditches or creeks are then carried to the waterway by
stormwater. Groundwater is also a pathway for contaminants to reach the LDW.
In addition to industrial use, residential areas near and on the LDW include the neighborhoods of South
Park and Georgetown and four marinas that permit live-aboard vessels. Though much habitat has been lost,
many fish and wildlife species inhabit the LDW, particularly in the Kellogg Island area. Salmon runs
passing through the LDW provide a valuable commercial and cultural resource for the Muckleshoot and
Suquamish Tribes.
Risks Posed by Contaminants
Multiple hazardous substances have been and continue to be discharged into the LDW and remain in the
water column and waterway sediments. Once in the water and sediment, the contaminants may be taken up
by organisms, including bottom-dwelling organisms (also called benthic invertebrates), fish, and shellfish.
The consumption of these organisms by larger fish, shellfish, and wildlife provides a mechanism for the
contaminants to move from the sediment and water up through the food chain. This poses threats to human
health and the environment when people and wildlife consume resident fish and shellfish from the LDW.
People and wildlife may also face risks from direct contact with contaminated LDW sediments.
Hazardous substances that pose unacceptable risk to human health and the environment are called
contaminants of concern or COCs in this Proposed Plan. The four COCs that pose the greatest risk to
human health are polychlorinated biphenyls (PCBs), arsenic, carcinogenic polynuclear aromatic
hydrocarbons (cPAHs)1, and dioxins/furans. Forty-one hazardous substances are of concern because they
are found at concentrations shown to be toxic to bottom-dwelling organisms; for example, phthalates. Of
the COCs found in LDW sediments, PCBs are the most widespread.
Remedial Investigation/Feasibility Study
In December 2000, the City of Seattle, King County, the Port of Seattle, and The Boeing Company
(Boeing), collectively known as the Lower Duwamish Waterway Group (LDWG), were issued an
Administrative Order on Consent jointly by EPA and Ecology, requiring them to conduct a remedial
investigation/feasibility study (RI/FS) pursuant to both CERCLA and Washington State's Model Toxics
Control Act (MTCA). During the RI, LDWG compiled and analyzed available data from numerous
investigations conducted prior to 2000, collected extensive additional data, conducted preliminary human
health and ecological risk assessments, and identified areas of greater contamination to be considered for
early cleanup. The Final Lower Duwamish Waterway Remedial Investigation Report (RI Report) was
completed in 2010. The RI included an assessment of risks to human health and the environment posed by
the contamination, and identified additional areas that require cleanup. In the Final Lower Duwamish
Waterway Feasibility Study (FS Report), completed in 2012, LDWG developed alternatives for cleanup of
the in-waterway portion of the Site. Also in 2012, LDWG developed two memoranda to supplement the FS,
which consider refinements to the alternative being considered as the Preferred Alternative (see Key
Documents on page 109). EPA and Ecology jointly provided oversight for the RI/FS.
1. cPAHs consist of a subset of seven PAHs which EPA has classified as probable human carcinogens:
benz[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenz(a,h)anthracene,
and indeno(l,2,3-cd)pyrene.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
2.1 Cleanup Activities Planned and Completed to Date
King County completed two cleanups of contaminated sediment in the LDW before and a few years after
the start of the RI/FS under a 1991 CERCLA Natural Resource Damages Consent Decree, to address
contamination from CSOs in Elliott Bay and the LDW:
• In 1999, 5,190 cubic yards (cy) of PCB-contaminated sediments outside the Norfolk CSO were
dredged by King County. The area was then backfilled. (A small area of PCB-contaminated sediments
inshore of this cleanup was excavated [60 cy] and capped by Boeing under Ecology's Voluntary
Cleanup Program in 2003.)
• In 2003 and 2004, a 7-acre area around the Duwamish/Diagonal CSO/SD was dredged (68,000 cy) and
capped. The COCs that triggered this action were PCBs, mercury, bis(2-ethylhexyl)phthalate (BEHP)
and butyl benzyl phthalate. In 2005, a 6-inch layer of clean sand was placed over an additional area that
had elevated PCB concentrations following cleanup.
The first phase of the RI identified additional areas with high levels of contamination that warranted early
cleanup action, called Early Action Areas (EAAs). Five EAAs were identified, including the two King
County cleanups described above. Three of the cleanups have been completed (the King County cleanups
described above, and the Slip 4 cleanup described below), and two more will be completed (also described
below) before the Preferred Alternative described in this Proposed Plan is implemented. Together, the
cleanups at these five EAAs (Figure 1) cover 29 acres, and address some of the highest levels of
contamination found in the LDW. Completion of the EAA cleanups will reduce the LDW-wide surface
area-weighted average sediment PCB concentration by an estimated 50%.
• Slip 4: Approximately 10,000 cy of PCB-contaminated sediments were dredged and 3.4 acres were
capped with clean sand, gravel, and granular activated carbon amended filter material, from October
2011 through January 2012, by the City of Seattle under an EPA Administrative Order and Settlement
Agreement on Consent (Consent Order).
• Terminal 117: Soils on the upland portion of T-l 17 with elevated concentrations of PCBs were
removed by the Port of Seattle with EPA oversight pursuant to separate Consent Orders issued by EPA
in 1999 and 2006. Upland cleanup of associated yards, streets, and rights of way will be completed by
the City of Seattle in 2013. Cleanup of T-l 17 EAA PCB-contaminated sediments are projected to be
completed by the Port and City in 2014 under an EPA Consent Order issued in June 2011.
• Boeing Plant 2/Jorgensen Forge: Adjacent areas of sediment contamination off shore of the adjacent
Boeing Plant 2 and Jorgensen Forge facilities will be cleaned up starting in 2013, now that sufficient
source control actions have been completed at the upland facilities. During the LDW remedial
investigation, EPA initially identified these areas as one EAA, but they are being addressed as separate
actions pursuant to separate EPA decision documents and Consent Orders under different laws that
require implementation coordination. Boeing Plant 2 contaminated sediments will be addressed under a
Resource Recovery and Conservation Act (RCRA) Consent Order issued to Boeing in January 1994.
Sediments contaminated with metals and other hazardous substances at Jorgensen Forge will be
cleaned up under a 2012 CERCLA removal Consent Order. EPA anticipates completion of both these
early actions by 2015.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
The following timeline provides a summary of LDW activities to date.
Lower Duwamish Waterway Timeline
1999 Cleanup was completed at the Norfolk CSO
2000 A Consent Order was issued by EPA and Ecology requiring LDWG to conduct the RI/FS
2001 LDW was listed as a Superfund site
2002 LDW was listed by Ecology as a cleanup site under MTCA
EPA and Ecology signed a Memorandum of Understanding (MOU) designating EPA as the lead for in-waterway
sediment cleanup, and Ecology as the lead for source control. The MOU was revised in 2004.
Ecology initiated the Source Control Work Group
2003 The LDW Phase 1 Rl was completed, and additional cleanup was conducted at the Norfolk CSO
2004 Ecology issued its Source Control Strategy
2005 Cleanup was completed at the Duwamish/Diagonal CSO/SD
2010 The Final LDW Rl was completed
2010 EPA issued an Action Memorandum (cleanup plan) for the T-117 EAA
2011 EPA issued a RCRA corrective action Final Decision (cleanup plan) for Boeing Plant 2 sediment
EPA issued an Action Memorandum for Jorgensen sediments and shoreline bank soils
2012 Cleanup was completed at the Slip 4 EAA
The Final LDW FS was completed
2013 Cleanup started at Boeing Plant 2
2.2 Source Control Investigations and Actions Completed to Date
Ecology is the lead agency for identifying direct and indirect sources of contaminants to the LDW Site.
Ecology uses its regulatory authority and works with other governments that have regulatory authority
(EPA, King County, City of Seattle, and Port of Seattle), also referred to as the Source Control Work
Group (SCWG), to control ongoing sources to the extent possible. The SCWG began its work in 2002, with
the goal of identifying, prioritizing, and controlling sources of contamination to the LDW before the
cleanup discussed in this Proposed Plan is completed.
Members of the SCWG performed numerous investigations to identify ongoing sources of contaminants.
These include:
• Compiling a water-wide summary of potential sources and investigating those potential sources.
• Developing Source Control Action Plans for each of the Source Control Action Areas that drain to the
LDW. Each plan identifies the authorities, tools, and milestone accomplishments for controlling the
sources and identifies criteria or other goals that determine effectiveness and completeness of source
8
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Proposed Plan — Lower Duwamish Waterway Superfund Site
control actions within each drainage basin. Ecology (with the SCWG) has identified 24 distinct
drainage basins that drain to the LDW, and has completed Source Control Action Plans for 20 of them.
• Tracing sources by sampling solids within storm drains and catch basins for contaminants. This helps
identify facilities where historical, unidentified, or illegal disposal of contaminants has occurred or is
occurring, making the facility an active source of contaminants affecting the LDW.
• Investigating and addressing contamination at upland facilities, including those contributing
contamination to the LDW via groundwater, stormwater, soil erosion, or air deposition.
• Developing and implementing other studies to identify ongoing sources, including: inputs to the
Green/Duwamish River; inputs due to outfalls and other lateral sources; and inputs of PCBs in or from
building materials in the source area.
Ecology, with the SCWG, has made substantial progress in finding, investigating and controlling both
historical and ongoing sources to the LDW, though more work remains. The summary on the next page
highlights numerous ongoing LDW source control actions. More detailed information about the source
control studies and work to date can be found on Ecology's website at:
http://www.ecy.wa.gov/programs/tcp/sites_brochureAower_duwamishAower_duwamish_hp.html.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Summary of Source Control Actions To Date
All of the work conducted to date and summarized below involved one or more of the following elements: source control investigations, site
assessment and cleanup, inspections, source tracing, sampling, and monitoring. For comprehensive accounts, and up to date information,
check the most recent Source Control Status Reports on Ecology's website at
http://www.ecy.wa.gov/programs/tcp/sites_brochure/lower_duwamish/lower_duwamish_hp.html.
One hundred ninety-six confirmed or suspected contaminated upland facilities have been identified within the LDW drainage basin, although
only some of those are sources of contaminants to the LDW.
Thirteen facilities along or near the LDW are under agreed orders for investigation and cleanup administered by Ecology's Toxic Cleanup
Program:
- Jorgensen Forge Corporation - North Boeing Field/Georgetown Steam Plant
- 8801 East Marginal Way (former Paccar site) - Fox Avenue/Great Western Chemical
- South Park Landfill - Glacier NW/Reichhold
- Crowley Marine Services - Duwamish Shipyard
- Industrial Containers/Trotsky/Northwest Cooperage - Douglas Management Properties
- Boeing Isaacson-Thompson - Port of Seattle Terminal 115 North
- Duwamish Marine Center
Five additional facilities in the LDW source area are under agreed orders for investigation and cleanup administered by Ecology's Hazardous
Waste Treatment and Reduction (HWTR) program:
- Art Brass Plating - Blaser Die Casting
- Capital Industries - General Electric — Dawson Street Plant
- Philip Services Georgetown
Ecology has conducted site investigations at:
- South Park Marina (former A and B Barrel) - Basin Oil
- Washington State Liquor Control Board Warehouse - Douglas Management Company
- Industrial Container Services (formerly Northwest Cooperage)
Four voluntary cleanups under MTCA are occurring or have been completed at:
- Boeing Developmental Center - Port of Seattle Terminal 106/108
- General Services Administration — Federal Center South - City of Seattle 7th Ave Pump Station
(Approximately ten other voluntary cleanups have been completed or are occurring within the LDW Source Area at facilities not adjacent to the
LDW)
Eight facilities along or near the LDW are under an EPA cleanup process:
- Boeing Plant 2 (RCRA) - Jorgensen Forge shoreline (CERCLA)
- Rhone-Poulenc (RCRA) - Port of Seattle Terminal 117 (CERCLA)
- Boeing Electronics Manufacturing Facility (CERCLA) - Tully's/Rainier Commons (Toxic Substances Control Act)
- 24" stormwater outfall Boeing/Jorgensen property line (CERCLA)
- North Boeing Field/King County International Airport Storm Drain Treatment System (CERCLA)
In addition:
• Since 2003, the City of Seattle and King County have completed more than 3,000 inspections at nearly 1,400 businesses in the
LDW area. In addition, they have collected more than 800 sediment samples from storm drains and combined sewer systems to
help identify and characterize sources discharging to the municipal storm and wastewater collection systems.
• In 2008, Ecology signed an interagency agreement with the City of Seattle to expand source tracing sampling. As part of this
agreement, Seattle Public Utilities installed twenty additional sediment traps in the LDW study area, including areas on King County
International Airport and unincorporated King County.
• From October 2009 through November 2012, Ecology's Lower Duwamish Urban Waters Initiative inspection team has completed
230 water quality inspections and 191 hazardous waste inspections.
• Approximately 100 facilities in the LDW drainage basin have wastewater discharge permits from Ecology; approximately 90 facilities
are regulated under a general industrial stormwater permit; two active facilities have individual industrial wastewater discharge
permits; two facilities operate under a general permit for boatyards; and four facilities operate under a general permit for sand and
gravel facilities.
• Four local governments have municipal separate stormwater general discharge permits (Phase I for the city of Seattle and King
County, and the Port of Seattle as a secondary permittee; and Phase II Western Washington for the city of Tukwila).
• Two local governments (the city of Seattle and King County) have individual discharge permits for their combined sanitary sewer and
stormwater systems.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
2.3 Public Involvement
Public involvement is a cornerstone of EPA's and Ecology's LDW work. In 2002, EPA and Ecology
developed a community involvement plan to promote meaningful involvement of the public during the
investigation and cleanup of the LDW. This plan was developed based on interviews with community
members and identified stakeholders. Throughout the RI/FS process, EPA and Ecology have regularly
held public meetings and have attended community and advisory group meetings. The Agencies hold
quarterly stakeholder meetings to provide updates on the RI/FS, cleanup of the EAAs, and source control
activities. EPA and Ecology have consistently sought input from the Tribes, community groups, and
natural resource agencies when reviewing and commenting on sampling plans, the human health and
ecological risk assessments, and other RI/FS documents. Other community involvement activities have
included mailing fact sheets, providing opportunities for public comment on the RI and FS Reports,
providing information about EPA's work at the Site at annual community festivals, and providing updates
at neighborhood meetings. EPA and Ecology used input from a 2010 public review of the draft FS to
finalize the FS and develop this Proposed Plan. EPA provides technical assistance grants to the
community advisory group for the Site, the Duwamish River Cleanup Coalition/Technical Advisory
Group. This organization reviews information about the Site and shares it with community members.
EPA will continue to consult with Ecology and the Muckleshoot and Suquamish Tribes and engage with
the community throughout design, construction, and long-term monitoring of the remedy.
2.4 Involvement by Federally Recognized Tribes
The LDW is actively used by the Muckleshoot Tribe as part of their usual and accustomed fishing area,
and the Suquamish Tribe fishes the area north of the Spokane St. Bridge, immediately north of the LDW.
Consideration of how Tribal members may be exposed to contaminants in the LDW while engaging in
seafood harvest activities has been a primary factor shaping the assessment of human health risks. The
Tribes, as sovereign nations, have engaged in government to government consultations with EPA on the
cleanup process. The Tribes have also broadly and actively participated in meetings determining the
course of the cleanup to date.
2.5 Environmental Justice Analysis
In conjunction with the FS , in response to comments on the 2010 draft FS, an Environmental Justice (EJ)
Analysis for the LDW was conducted and a report was produced by EPA (Appendix B). EPA defines
environmental justice as "the fair treatment and meaningful involvement of all people regardless of race,
color, national origin, or income with respect to the development, implementation, and enforcement of
environmental laws, regulations, and policies." The purpose of the EJ Analysis was to 1) screen for EJ
concerns, and 2) identify disproportionate adverse impacts from the cleanup alternatives and the Preferred
Alternative and, if found, provide recommendations to mitigate such impacts. The information and
recommendations from the EJ Analysis have been considered in the development of this Proposed Plan
and will also be considered for the ROD. Recommendations from the EJ analysis that fall outside of the
scope or authority of CERCLA may be referred to another agency for their consideration.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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Proposed Plan — Lower Duwamish Waterway Superfund Site
3 Lower Duwamish Waterway Setting
The LDW, originally the natural meandering estuary at the confluence of the Green/Duwamish River
system and Elliot Bay, was modified in the early 1900s to become an engineered navigation channel for
commercial use, termed a waterway, from RM 0 to RM 4.7. The in-waterway portion of the LDW
Superfund Site extends from RM 0 to RM 5, encompassing approximately 441 acres. Much of the natural
wetland habitat and mudflat areas associated with the original Duwamish River estuary are no longer
present as a result of the waterway construction and subsequent upland development.
The LDW supports major shipping activities for containerized and bulk cargo. Approximately 40 berthing
areas are located along the LDW. The central portion of the waterway is maintained as a federal
navigation channel by the US Army Corps of Engineers (USACE). The navigation channel is maintained
at authorized navigable depths of 30 ft below "mean lower low water" (-30' MLLW)2 from Harbor Island
to the First Avenue South Bridge (RM 2), at -20 feet MLLW from the First Avenue South Bridge to Slip
4 (RM 2.8), and at -15 ft MLLW from Slip 4 to the Upper Turning Basin (RM 4.7). Depths outside the
navigation channel immediately south of Harbor Island at the mouth of the waterway are as deep as -47 ft
MLLW. To maintain navigation depths, the USACE dredges the upstream portion of the navigation
channel every one to three years. The area typically dredged is the Upper Turning Basin and downstream
to approximately RM 4. In addition, private parties periodically dredge berthing areas to maintain depths
for their own purposes, typically shipping and marina uses.
Outside of the navigation channel, the LDW banks are comprised of sloped subtidal embankments,
shallow subtidal and intertidal areas (including five slips along the eastern shoreline and three
embayments along the western shoreline), and Kellogg Island near the downstream end. The shoreline
consists primarily of hardened surfaces, including riprap, aprons for piers, and sheet pile walls, with some
beaches and intertidal habitat remaining in isolated patches.
3.1 Land Use
The LDW and surrounding area is Seattle's primary industrial corridor. Industries currently operating
along the Duwamish include marine construction, boat manufacturing and repair, marinas, cement
manufacturing, cargo handling and storage, paper and metals fabrication, food processing, airplane parts
manufacturing and a municipal airport. However, the Duwamish estuary subwatershed (extending from
RM 11 to Elliott Bay) of the Green/Duwamish watershed has more residential land use (36%) than
industrial and commercial land use combined (29% combined; 18% and 11%, respectively). Eighteen
percent of the subwatershed is used for right-of-way areas (including roads and highways); while 17% is
open/undeveloped land and parks.
Two neighborhoods, South Park and Georgetown, are located to the west and east, respectively, of the
LDW. EPA and Ecology have identified environmental justice concerns in the South Park and
Georgetown neighborhoods in accordance with Executive Order 12898, Federal Actions to Address
2. The LDW has two high tides and two low tides each day. MLLW is the average lowest daily low-water height
and mean higher high water (MHHW) is the average highest daily high-water height, averaged over many years.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Environmental Justice in Minority Populations and Low-Income Populations. As noted in EPA's
Environmental Justice Analysis for the Lower Duwamish Waterway Superfund Cleanup (EJ Analysis),
included as Appendix B to this Proposed Plan, incomes in South Seattle where these neighborhoods are
located are approximately 50% lower and percentages of minority populations are significantly higher
than in the City of Seattle (the population of the City of Seattle is approximately 30% minority, compared
to the LDW corridor which is approximately 50% minority). This area also has higher rates of asthma
hospitalizations and rates of other chronic diseases such as diabetes than other Seattle neighborhoods and
King County as a whole. These neighborhoods support a mixture of residential, recreational, commercial,
and industrial uses.
3.2 Waterway Use
The LDW supports considerable commercial navigation and is also used for various recreational activities
such as boating, kayaking, fishing, and beach recreation. Several public parks and publicly accessible
shoreline areas exist within the LDW, and there are plans to create additional recreational and habitat
opportunities in the LDW corridor. To inform these waterway users about risks from eating fish and
shellfish, the Washington Department of Health (WDOH) provides advisories (described in Seafood
Advisories for the Lower Duwamish Waterway, below).
The LDW is one of the locations of the Muckleshoot Tribe's commercial, ceremonial, and subsistence
fishery for salmon, as part of its usual and accustomed fishing area. The Suquamish Tribe actively
manages aquatic resources north of the Spokane Street Bridge, just north of the LDW study area.
Four marinas and two public parks (Terminal
107/Herring's House and Duwamish
Waterway Park) are located along the LDW,
and several other access points allow the
public to enter the LDW for recreational
purposes. A third, non-Federally recognized
Tribe, the Duwamish Tribe, uses parks along
the LDW for cultural gatherings and canoe
launching. A human access survey conducted
along the LDW shoreline as part of the RI
survey identified the following uses:
launching and hauling out hand-powered boats or motorboats, walking, fishing, swimming, and
picnicking. Although recreational use may increase at some point in the future, the primary uses of the
waterway and surrounding area are anticipated to remain commercial (navigation and fisheries),
industrial, and residential (Figure 2).
3.3 Ecological Communities in the LDW
The LDW is home to a diverse ecology, with abundant resident and non-resident fish and shellfish,
bottom-dwelling organisms, marine mammals, and birds.
Seafood Advisories for the Lower Duwamish Waterway
The Washington State Department of Health (WDOH) currently
recommends no consumption of fish and shellfish (other than
salmon) from the LDW. The WDOH maintains a web site and
provides publications and other educational forums that cover
healthy eating and seafood consumption. In addition, the seafood
consumption advisories are posted on signs at public access
locations within the LDW. More information can be found at
http://www. doh. wa.gov/fish.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Fishing
Fishing1
Beach 6\
T-108/Diagonal
Ave S Public
Derelict Barge
Removed
1 st Ave S Boat Ramp
Beach 4
Employee access only, but public
could access at low tide.
Gateway North/
8th Ave S Street End
Fishing
Picknicking
Habitat Restoration
Hand Boat Launch
Swimming
Beach 5
Fishing
Picknicking
Habitat Restoration
Jogging Path
Swimming
S Portland Street End
Fishing
Picknicking
Hand Boat Launch
Jogging Path
Swimming
Biking
Duwamish
Waterway
Picnicking
Fishing
Shellfish Harvesting
Swimming
Jogging Path
Birding
Biking
Hand Boat Launch
Habitat Restoration
{
GSA Marsh I Habitat Restoration Area
Park
Beach Play Area (44 acres)
Potential Clamming Area (105 acres)
Intertidal Area (+11.3 to -4 Ft MLLWM128 acres)
Subtotal Area <> -4 ft MLIW)(313 acres)
Road or Bridge
—— Navigation Channel
River Mile Marker
Port
Turning Basin and
Coastal America Sites
Legend
Picknicking
Fishing
Habitat Restoration
Jogging Path
Birding
Hand Boat Launch
Fishing
Birding
Beach
4.3
Muckleshoot Tribe/
Kenco Marine
Shellfish Harvesting
Fishing
Picknicking
Habitat Restoration
Hand Boat Launch
Birding
Jogging Path
Swimming
Fishing
Hand Boat Launch
Hamm Creek
Upper
Turning
House Park
Figure 2. LDW Parks, Beach Play, and Potential Clamming Areas
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Several bottomfish (sole, sculpin, flounder) and water column fish (perch and herring) are abundant in the
LDW, as are salmon. The Green/Duwamish River system supports eight species of salmonids: coho,
Chinook, chum, sockeye, and pink salmon, plus cutthroat trout, both winter- and summer-run steelhead,
and bull trout. Juvenile Chinook and chum have a residence time in the LDW from several days to two
months; coho are in the LDW for only a few days; and sockeye are rare in the LDW. Salmon found in the
LDW spawn mainly in the middle reaches of the Green River and its tributaries. The juvenile outmigration
generally starts between March and June. Outmigration usually lasts through mid-July to early August.
Puget Sound Chinook salmon are listed as threatened under the federal Endangered Species Act (ESA).
Other relevant fish species listed as threatened under the ESA include the coastal Puget Sound bull trout
and the Puget Sound steelhead. The LDW is designated as critical habitat for bull trout and Chinook
salmon. The bald eagle was delisted in 2007 under the ESA but is protected under the Bald and Golden
Eagle Protection Act, and under the Migratory Bird Treaty Act.
Typical of most estuaries, the benthic invertebrate community is dominated by annelids (worms), mollusks
(clams and snails), and crustaceans (e.g., shrimp and crabs). Dungeness and other crabs are present in the
LDW, although their distribution is generally limited to the portions of the LDW with higher salinity.
The common shorebirds and wading birds observed in the LDW are sandpipers, killdeer, and great blue
herons. Bald eagles, ospreys, and great blue herons nest on or near the LDW and use the LDW for foraging.
The LDW provides habitat for mammal species including harbor seals, sea lions, and river otters.
3.4 Sediment Transport and Deposition
Human activity has greatly influenced water and sediment movement in the LDW. Rivers that historically
flowed into the upstream Green River were diverted in the early twentieth century, reducing the volume of
water entering the LDW by approximately 70%. Water flows are now managed by the Howard Hanson
Dam, constructed in 1961, approximately 65 miles upstream. In addition, the LDW has been widened and
deepened to permit navigation. As a result, peak flows are much smaller with maximum flows rarely
exceeding 12,000 cubic feet per second. The reduction in peak flows results in less erosion and more
deposition of sediments.
The LDW is a two-layer salt wedge estuary, with outflow that is mostly freshwater originating from the
Green/Duwamish River at the surface, and tidally-influenced salt water from Puget Sound entering the
LDW at the mouth of the waterway beneath it. The saltwater "wedge," or interface between fresh water at
the surface and salt water at depth, is always present from RM 0 to RM 2.2, and is periodically present
between RM 2.2 and RM 4, depending on tide height and river flow. Between RM 4 and RM 5 freshwater
is usually predominant, although the saltwater wedge can extend through this area when the tide is high and
river flow is low. LDW tidal fluctuations average about 11 feet. The presence of the salt water layer in
some portions of the LDW helps reduce sediment scour during high river flows.
Sediment Transport Model
A three-dimensional sediment transport model (STM) was developed to simulate water and sediment
movement over a wide range of flow and tidal conditions to inform the type of sediment cleanup
technologies that would be appropriate for the area. The model estimated that, on average, more than
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Proposed Plan — Lower Duwamish Waterway Superfund Site
200,000 metric tons of sediment enters the LDW each year. About 50% of the incoming sediment deposits
within the LDW. The rest is exported further downstream to Elliott Bay. Approximately 50% of the
sediment that settles in the LDW is removed by periodic navigational maintenance dredging. The annual
average amount dredged from the LDW by the US Army Corps of Engineers (USACE) is 51,000 metric
tons, mostly in the Upper Turning Basin. Thus, approximately 25% of the incoming sediment remains in
the LDW after dredging.
Based on the STM, approximately 99% of the sediment entering the waterway is from upstream. The other
approximately 1% is directly discharged into the LDW via storm drains, CSO outfalls, and small streams.
Although direct discharges to the LDW only account for approximately 1% of the sediment load to the
LDW, the contaminant concentrations in these sediments are much higher than in the sediments coming in
from upstream. This often causes elevated contaminant concentrations in localized areas around outfalls.
These higher concentrations are being addressed as part of source control (see Section 2.2).
Deposition and erosion predicted by the model, along with estimated vessel scour areas (not predicted by
the model), are illustrated in Figure 3. The STM results indicate that, overall, there is more deposition of
sediment than erosion in the LDW. Some areas are more erosional and some are more depositional. Erosion
of the sediment bed by river flow (high-flow scour) is limited, even during high-flow events. Most bed
erosion due to high-flow scour is less than 10 centimeters (cm) in depth and maximum estimated net
erosion depths are 22 cm. Vessels may cause localized scour to depths greater than 22 cm but likely less
than 60 cm. The STM's predictions are corroborated by sediment contaminant concentration data collected
in the same locations overtime, which indicate that natural recovery (as described in Section 8.2.1) is
occurring in some areas of LDW.
Bed Composition Model
A second model, the bed composition model (BCM), was used to estimate future COC concentrations in
LDW sediments. The BCM used predictions of sediment movement from the STM, data on sediment
contaminant concentrations in the LDW and in sediment entering the LDW from the Green/Duwamish
River, and data on other sediment inputs to the LDW from ditches, streams, and municipal discharges in
the LDW basin. The BCM provided predictions of approximate future sediment contaminant
concentrations that would exist after implementation of each of the proposed cleanup alternatives.
Uncertainty and Sensitivity Analyses
Uncertainty and sensitivity analyses were performed for the STM and for the BCM. The primary sources of
uncertainty in the physical and chemical model predictions are: 1) COC concentrations in incoming
sediments from upstream and lateral sources, 2), the rate of net sedimentation/burial from incoming
sediment loads, and 3) the potential for deep disturbances of subsurface contaminated sediments by
mechanisms such as vessel (propeller wash) scour and earthquakes. While long-term projections of
contaminant concentrations and the time to reach the lowest model-projected concentrations must be
viewed in light of these uncertainties, the STM and BCM modeling, along with a subsurface-disturbance
analysis provided in the FS, provide a sufficient basis for comparison of alternatives and selection of a
Preferred Alternative.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Legend
Annual Net Sedimentation Rate From STM (cm/yr)
Net Erosion
*0.5
>0.5-1.0
>1-2
>2-3
>3
STM Grid Cell
~ Outside of Model Domain
tZZI High-Flow Scour (> 10 cm)(30 year simulation)
Evidence of Propeller Wash Scour
] Early Action Area
Road
Navigation Channel
River Mile Marker
Upper
Turning
Basin
Figure 3. Potential Scour Areas and Estimated Net Sedimentation Rates
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Proposed Plan — Lower Duwamish Waterway Superfund Site
3.5 Extent of Contamination
Numerous investigations have been conducted to determine the nature and extent of contamination in the
LDW. The National Oceanic and Atmospheric Administration (NOAA) and EPA conducted waterway-
wide investigations of the LDW in 1997 and 1998, respectively. At least 25 smaller, location-specific
investigations have been conducted
by King County, the City of Seattle,
Boeing, and other private entities.
LDWG completed Phase 1 of the RI
in 2003. This study compiled and
analyzed pre-existing data,
identifying areas of higher
contamination to be considered for
early cleanup. LDWG collected
extensive additional data during
Phase 2 of the RI through 2009.
These additional data, new data
collected by other parties, and Phase
1 data were used to develop the RI
Report, which was completed in
2010. The RI study area extended to
RM 7, but the study area was
reduced to the lower five miles in
the FS because RI data showed very
low levels of contamination
upstream of RM 5.
The nature and extent of hazardous
substance contamination was
evaluated in the RI based on the concentration of contaminants in approximately 1,500 surface sediment
samples (top 10 cm of the river bed), 900 subsurface sediment samples, 420 fish and shellfish tissue
samples, 480 surface water samples, 110 seep samples, and 90 porewater samples. Toxicity tests were
performed on 76 surface sediment samples. Data collected in multiple investigations between 1990 and
April 2010 were incorporated into the RI dataset. Of these, approximately 900 samples were collected as
part of the RI in 2004 - 2006. An additional 47 samples were collected during the FS in 2009 - 2010.
The results of these investigations for sediments, fish and shellfish tissue, and surface water are described
below.
3.5.1 Surface and Subsurface Sediments
Table 1 summarizes minimum and maximum detected concentrations, average concentrations, and
detection frequencies for PCBs, arsenic, cPAHs, and dioxins/furans in surface and subsurface sediments.
These contaminants account for the majority of human health risks from contamination in the LDW.
What Are the Most Harmful Contaminants
in the Lower Duwamish Waterway?
There are many hazardous substances found in LDW sediments, fish, and
shellfish. Most of the human health risk comes from these four:
PCBs are manmade chemicals that were banned in the late 1970s. PCBs were
widely used in coolants and oils, paints, caulking, and building material. PCBs
stay in the environment for a long time and can build up in fish and shellfish.
Children exposed to PCBs may develop learning and behavior problems later
in life. PCBs are known to impact the immune system and may cause cancer in
people who have been exposed to them over a long time.
Arsenic is associated with industrial uses like lumber treatment and watercraft
repair. Industrial activities have spread additional arsenic over much of the
Puget Sound Region. It is also naturally present at low levels in Puget Sound
area rock and soil. Long-term exposure to toxic forms of arsenic may cause
skin, bladder, and other cancers.
PAHs are formed during the burning of substances such as coal, oil, gas,
wood, garbage and tobacco and during the charbroiling of meat. Historical
industrial activities are a known source of PAHs, as well as creosote treated
timber. Long periods of breathing, eating, or having skin contact with high
levels of some of the PAHs may increase a person's risk of cancer.
Dioxins/furans are by-products of burning (either in natural or industrial
settings), chemical manufacturing, and metal processing. Historically,
dioxins/furans were byproducts of pentachlorophenol (used in wood treating),
pesticide, and PCB production. Dioxins last a long time in the environment
and, like PCBs, can build up in fish and fatty foods. Specific toxic effects
related to dioxins include: reproductive problems, problems in fetal
development or in early childhood, immune system damage, and cancer.
19
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Table 1. Statistical Summaries for Human Health COCs in Sediment
Summary Statistics for Sediment in the LDW
Total Number of
(RM 0 to RM 5)
Sediment Samples
Spatially-Weighted
Average
With
Minimum
Calculated
Maximum
Concentration
Detected
Data Type/Contaminant
Detected
Mean
Detected
(SWAC)
Total
Values
Surface Sediment
PCBs (|jg/kg dw)a
2.2
1,100
220,000
350
1,392
1,309
Arsenic (mg/kg dw)
1.2
17
1,100
16
918
857
cPAHs (|jg TEQ/kg dw)b
9.7
460
11,000
400
893
852
Dioxins/Furans (ng TEQ / kg dw)c
0.25
42
2,100
26
123
119
Subsurface Sediment
PCBs (|jg/kg dw)
0.52
2000
890,000
n/a
1,504
1,131
Arsenic (mg/kg dw)
1.2
30
2,000
n/a
531
453
cPAHs (|jg TEQ/kg dw)b
1.2
370
7,000
n/a
542
449
Dioxins/Furans (ng TEQ / kg dw)c
0.15
17
190
n/a
64
64
NOTE: Based on FS baseline dataset, which includes sampling data from all EAAs except the Duwamish/Diagonal CSO/SD and
Norfolk CSO EAAs (these cleanups were completed before the start of the FS).
a. Two PCB samples, at the inlet at RM 2.2, were considered outliers and were not included in the data considered; their
detected concentrations were 230,000 and 2,900,000 pg/kg. Mean and SWAC for PCBs were calculated without the two
outliers; if the outliers were included, the mean would be 3,400 |jg/kg dw and the SWAC would be 1,300 |jg/kg dw.
b. The cPAH TEQ was calculated using compound-specific potency equivalency factors.
c. The dioxin/furan TEQ was calculated using World Health Organization's mammalian toxic equivalent factors.
Surface Sediments
Based on RI data, PCBs are the most widespread contaminant in LDW surface sediment; they were detected
at 94% of the locations where samples were analyzed for PCBs. The distribution of PCBs in LDW surface
sediment is shown in Figure 4.
To identify areas where COCs were present at concentrations toxic to benthic invertebrates, the RI/FS used
the Washington State Sediment Management Standards (SMS), which are explained in What are the
Sediment Management Standards? on page 37. In the SMS, the numerical sediment quality standards (SQS)
are contaminant concentrations below which no adverse effects on benthic invertebrate organisms are
expected. The SMS also establishes cleanup screening levels (CSLs), higher levels for the same
contaminants at which minor effects are expected. The SMS regulations also allow use of site-specific
biological effects criteria (based on toxicity testing or benthic abundance data) to determine whether a
location passes or fails the SQS or CSLs.
Surface sediment samples from a subset of locations were tested for both contaminant concentrations and
biological effects. Sample locations where SQS or CSL chemical numerical standards were exceeded but
biological criteria were not exceeded were designated as not exceeding the SQS or CSL—that is, the
determination of whether criteria are exceeded was based on biological criteria not chemical numerical
standards. It is important to note that risks to human health or to animals coming into contact with sediment
or eating fish and shellfish that live in the waterway are not addressed by either the SMS chemical
numerical standards or biological criteria. Those risks are addressed separately as described in this Plan.
20
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Legend
Predicted Total PCB Concentration (pg/kg dw)
I I *30
H >30-60
¦I >60-100
~ > 100-240
~ > 240 - 480 (>SQS)
~ > 480 - 720
I j > 720- 1.300
¦I > 1.300 (>CSL)
PCB Sample Location
Road
Navigation Channel
River Mile Marker
EZ2 Early Action Area (Cleanup not Complete)
CD Early Action Area (Cleanup Complete)
Notes:
1. SQS value of 240 pg/kg and CSL value of 1,300 pg/kg based
on conversion of 12 mg/kg OC and 65 mg/kg OC to dry weight values using 2% TOC.
2. Concentrations were interpolated from surface sediment data using
inverse distance weighting as described in Appendix A of the Feasibility Study.
Upper
Turning
Basin
Figure 4. PCB Distribution in Surface Sediment
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Legend
V7Z\ Early Action Area (Cleanup not Complete)
Early Action Area (Cleanup Complete)
SMS Status
> SQS and < CSL
Notes:
1. SMS status is assigned to match that for the highest exceedance status for
any contaminant for any point within the polygon. If a toxicity sample is
co-located with a chemistry sample, the toxicity data override the
chemistry results for that polygon.
2. Exceedance areas were generated by using the FS baseline dataset to generate
Thiessen polygons.
I > CSL
Road
Navigation Channel
River Mile Marker
Figure 5. SMS Status in Surface Sediment
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Figure 5 shows areas where neither SQS or CSLs were exceeded, areas where only SQS but not CSLs were
exceeded, and areas where CSLs were exceeded (and therefore SQS were exceeded also).
Forty-one hazardous substances were detected in LDW sediment at concentrations that exceed the chemical
SQS and were designated as COCs for benthic invertebrates. PCB concentrations in surface sediment
exceeded the SQS more frequently than any other COC (Figure 4), followed by BEHP, then butyl benzyl
phthalate. The locations where these exceedances occur and extent of these exceedances vary by COC.
Table 7 (on page 38, in the Ecological Risks section) provides summary information on surface sediment
contamination for these 41 COCs, including minimum and maximum detected concentrations, average
concentrations, and detection frequencies. In addition to contaminant concentrations, several other
parameters were measured during the RI. The percent fines (sum of clay and silt fractions) in surface
sediments ranged from 13 to 87% with an average of approximately 53%. The LDW-wide average total
organic carbon (TOC) content is 2%. Sediment grain size and TOC influence the quality of habitat for
benthic invertebrates and other organisms. Grain size is also important in determining whether sediments
will erode from or be deposited in the LDW. TOC influences the bioavailability of some organic
contaminants. Because of this, many organic contaminants are "normalized" to TOC in the SMS.
Subsurface Sediments
Detected contaminant concentrations were above the SQS for at least one of the SMS contaminants in 49%
of the subsurface sediment samples. The average thickness of subsurface sediments with COC
concentrations greater than the SQS is four feet. Of the COCs detected in subsurface sediments at
concentrations above the SQS, PCBs were detected most frequently (48%), followed by BEHP (25%).
Table 1 summarizes surface and subsurface sediment contaminant concentration data for the human health
COCs: PCBs, arsenic, cPAHs, and dioxins/furans.
3.5.2 Fish, Shellfish, and Benthic Invertebrate Tissue
The ranges of contaminant concentrations for all types of organisms and tissue types sampled during the
RI/FS (in some cases whole organisms and in other cases portions of the organisms were sampled), and the
general trends in tissue concentrations observed are summarized as follows:
• PCBs - Detected in almost all samples, ranging from 6.9 micrograms per kilogram wet weight (j^ig/kg
ww) to 18,400 (ig/kg ww. Mean PCB concentrations were highest for Dungeness crab hepatopancreas
("crab butter") and whole-body English sole, followed by whole-body shiner surfperch. Clam and crab
edible meat had much lower mean PCB concentrations, with mean PCB concentrations being lowest
for mussels.
• Inorganic arsenic - Detected in almost all samples, ranging from non-detect (< 0.003) to 11.3
milligrams per kilogram wet weight (mg/kg ww). Inorganic arsenic is the most toxic form for humans
and wildlife. Total arsenic was measured in sediments and water and inorganic arsenic was measured
in fish and shellfish tissue. Eastern softshell clams (the most abundant clam species found in the LDW)
had the highest average concentrations of inorganic arsenic, approximately 3 mg/kg ww. Clam
inorganic arsenic concentrations were 12- to 1500-fold greater than inorganic arsenic concentrations
found in other organisms.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
• Other COCs — Concentrations of cPAHs were highest in clam, mussel, and benthic invertebrate
tissue. Phthalates were frequently detected in clams and benthic invertebrates. Most other organic
hazardous substances were infrequently detected. Sampling for dioxin/fiirans in tissue was not included
as part of the RI because data that were already available indicated that dioxin/furan concentrations in
most Puget Sound fish and shellfish tissues would present unacceptable risk at the consumption rates
used in the human health risk assessment. No further data were needed for the human health risk
assessment, which assumed unacceptable risks due to dioxins/furans. Data were gathered from a small
number of dioxin/furan samples of skin-off English sole fillets collected near Kellogg Island by
Ecology in May 2007, after completion of the human health risk assessment.
Table 2 summarizes PCB, inorganic arsenic, cPAH, and dioxins/furan tissue concentrations in some of the
LDW fish and shellfish collected and analyzed in the RI.
Table 2. Summary of Selected Human Health COCs in Fish and Shellfish Tissue3
Contaminant and Tissue Type
Detection
Frequency
Concentration
Minimum
Mean
Maximum
PCBs (iug/kg ww)
English sole (fillet with skin)
26/26
170
860
2,010
Shiner surfperch (whole body)
78/78
20b
1,300
18,400"
Dungeness crab (edible meat)
14/17
15
130
300
Dungeness crab (whole body)
16/16
97
890
1,900
Clams (not depurated)
20/20
15"
130
580"
Inorganic Arsenic (mg/kg ww)
English sole (fillet with skin)
6/7
0.003
0.004
0.006
Shiner surfperch (whole body)
8/8
0.020
0.070
0.160
Dungeness crab (edible meat)
2/2
0.010
0.010
0.010
Dungeness crab (whole body)
2/2
0.022"
0.029
0.035
Clams
23/23
0.132
2.72
11.3
cPAHs (ijg TEQ/kg dw)
English sole (fillet with skin)
4/7
0.37"
0.35
0.53
Shiner surfperch (whole body)
24/27
0.37"
3.1
2.2
Dungeness crab (edible meat)
6/9
0.54"
3.7"
0.84"
Dungeness crab (whole body)
7/9
0.60
2.6
2.4
Clams
14/14
6.8
15
44
Dioxins/Furans (ng TEQ/kg dw)c
English sole (fillet without skin)
6/6
0.26
0.30
0.35
a. Section 5.1 describes the selection of human health COCs.
b. These data points are analytically estimated values.
c. The dioxin/furan data are from samples collected in a small portion of the LDW as part of a 2007 Ecology study, and were
not used in the LDW risk assessments.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Relationships among concentrations in tissue and concentrations in sediments for PCBs, arsenic, and
cPAHs were investigated in the RI. In species with small foraging ranges (clams, benthic invertebrates,
shiner surfperch, and staghorn sculpin), tissue PCB concentrations were higher in areas with higher
sediment PCB concentrations; in species with larger foraging ranges (English sole and crabs), tissue
concentrations did not show a clear relationship to sediment concentrations. Clams had the highest
inorganic arsenic and cPAH tissue concentrations, but no strong relationship was seen between sediment
concentrations and clam tissue concentrations of arsenic and cPAHs.
3.5.3 Surface Water
The water column, along with the contaminated sediments, is an important pathway for COCs to reach
benthic organisms, fish, and shellfish. LDW surface water was collected and analyzed by King County for
metals, semi-volatile organic compounds, and PCBs in 1996 and 1997 and for PCBs in 2005. For the
human health COCs, PCB concentrations in 2005 LDW surface water samples ranged from 0.13 to 3.2
nanograms per liter (ng/L). Arsenic concentrations ranged from 0.18 to 1.5 micrograms per liter ((.ig/L).
Of the cPAHs, chrysene had the highest concentrations, at 0.17 to 0.4 (ig/L. Dioxins/furans were not
measured in surface water due to the difficulty in detecting these contaminants in whole water samples.
EPA determined that more water quality sampling during the RI would not have affected the analysis of
human health or ecological risks, or have influenced the development of alternatives for the in-waterway
portion of the Site.
3.6 Background and Upstream COC Concentrations
Documenting background concentrations (concentrations at locations away from the Site and away from
any urban or contamination source) is important in the process of identifying cleanup goals. This section
describes how contaminant concentrations in sediments and in fish and shellfish in non-urban areas of
Puget Sound were used to estimate background conditions, and how upstream contaminant concentrations
were used in the BCM to estimate the concentrations of COCs in sediments that deposit in the LDW.
3.6.1 Sediment Background and Upstream Concentrations
When risk-based threshold concentrations (RBTCs, see Section 4) are below background, background
concentrations are used as Preliminary Remediation Goals (PRGs are COC concentrations EPA proposes
to select as cleanup levels in the ROD, see Section 7). In cases where applicable or relevant and
appropriate requirements (ARARs) for a CERCLA action allow cleanup to be considered complete when
background levels are reached, the response action generally should be carried out in accordance with the
ARAR. For this reason, whenever PRGs and cleanup levels at CERCLA sites in the State of Washington
are based on background levels, natural background levels as established in the MTCA are used3,
consistent with WAC 173-340-700(6)(d).
3. Generally, under CERCLA, cleanup levels are not set at concentrations below natural background levels.
Similarly, for concentrations of human-made (anthropogenic) contaminants, the CERCLA program normally does
not set cleanup levels below anthropogenic (human-influenced) background concentrations. The reasons for this
approach include cost-effectiveness, technical practicability, and the possibility that remediated areas could be
recontaminated by surrounding areas with elevated background concentrations.
25
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Proposed Plan — Lower Duwamish Waterway Superfund Site
MTCA (at WAC 173-340-200) defines the "natural background" level of a hazardous substance as the
concentration that is consistently present in an environment that has not been influenced by localized
human activities. Thus, under MTCA, a "natural background" concentration can be defined for human-
made compounds even though they may not occur naturally. For example, PCBs (human-made
compounds) can be picked up and carried by the winds and then deposited into an alpine lake that has not
been locally influenced by human activities, and the concentration of PCBs that is then consistently
present in that lake is the "natural background" level.
Although COC concentrations in suspended sediments from upstream were not used as background
concentrations in the RI/FS, they were used to estimate upstream COC concentrations to use as inputs to
the BCM.
Sediment Background COC Concentrations
Data from a 2008 EPA study of sediment contaminant concentrations in non-urban areas in Puget Sound
were used to characterize sediment natural background COC concentrations. Sediment samples were
collected at locations that are away from populated and industrial areas and known contaminated sites.
Summary statistics were then calculated for each of the four human health COCs. Table 3 summarizes
these data.
Table 3. Summary of PCB, Arsenic, cPAH, and Dioxin/Furan Data for Natural Background
Concentrations in Sediment
Human Health COC
Detection
Frequency
Concentration
Minimum
Maximum
Mean
Median
90th
Percentile
95th Percentile
Upper Confidence
Limit on the Mean
(UCL95)»
PCBs ([jg/kg dw)a
70/70
0.01
11
1.2
0.6
2.7
2
Arsenic (mg/kg dw)
70/70
1.1
21
6.5
5.9
11
7
cPAHs (|jg TEQ/kg dw)
61/70
1.3
58
7.1
4.5
15
9
Dioxins/Furans (ng TEQ/kg dw)
70/70
0.2
12
1.4
1.0
2.2
2
a. Only congener data were used, as there were few detected values in the Aroclor data
b. These values are rounded to one significant figure
Sediment COC Concentrations from Upstream of the LDW Study Area
Several datasets with sediment COC concentrations from upstream locations were evaluated for use in
estimating COC concentrations in suspended sediments entering the LDW from the Green/Duwamish
River. Because of the large volume of suspended sediments entering the LDW from the Green/Duwamish
River, these data were important input parameters for BCM-predicted estimates (see Section 3.4) of future
COC concentrations in the LDW after implementation of the cleanup alternatives evaluated in the FS.
26
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Datasets included:
• COC concentrations in Green/Duwamish River surface sediments and suspended sediments
immediately upstream of the Site from two 2008 Ecology studies. Surface sediments in the
Green/Duwamish River are generally much coarser than those found in the LDW. In order to match
the grain size of sediments that deposit in the LDW, only surface sediments with greater than 30%
fines were included.
• Sediment core data collected from the LDW Upper Turning Basin from 1991 to 2009 by the US
Army Corps of Engineers for maintenance dredging. The LDW Upper Turning Basin is a sink for
sediments entering the LDW from upstream. These data provide an indicator of suspended sediments
settling in the upper reach of the LDW.
Table 4 shows the mid-range estimates of upstream suspended sediment COC concentrations selected for
use in the BCM, for the four human health COCs. Each sampling technique may over- or underestimate
the COC concentrations in sediments entering the LDW. Best professional judgment was used to select
mid-range values used as upstream input values for the BCM, and also to select high and low values used
for sensitivity analysis.
Table 4. Estimates of Sediment and Suspended Sediment COC Concentrations of PCBs, Arsenic,
cPAHs, and Dioxins/Furans from Upstream of the LDW Study Area
Human Health COCs
Selected3
Upstream Value
Dataset and Statistic Used to Calculate
BCM Upstream Input Value
PCBs (|jg/kg dw)
36
Upper Turning Basin subsurface sediment data, mean
Arsenic (mg/kg dw)
9
Upstream Green/Duwamish River surface sediment data, mean
Carcinogenic PAH (|jg TEQ/kg dw)
73
Upper Turning Basin subsurface sediment data, mean
Dioxins/Furans (ng TEQ/kg dw)
4
Midpoint between the means of Green/Duwamish River surface
sediment and suspended sediment datab
a. These values were selected for use as inputs to the BCM.
b. No dioxin/furan data were collected in the Upper Turning Basin during the FS, so data from upstream samples were used.
3.6.2 Fish and Shellfish Tissue Background COC Concentrations
A dataset of COC concentrations in fish and shellfish tissue samples collected between 1991 and 2009
from non-urban areas in Puget Sound, away from populated and industrial areas and known contaminated
sites, was compiled for each of the four human health COCs (PCBs, inorganic arsenic, cPAHs, and
dioxins/furans) to define background COC concentrations. These non-urban Puget Sound fish and
shellfish tissue data, shown in Table 5, were used to set tissue PRGs (Section 7) when RBTCs were below
background.
Non-urban Puget Sound fish and shellfish tissue background COC concentrations are more uncertain than
sediment background concentrations. The dataset is comprised of data from various studies representing
different sampling and analysis methods. It also contains widely differing numbers of samples for the
27
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Proposed Plan — Lower Duwamish Waterway Superfund Site
various COCs and tissue types, depending on data availability and data quality considerations. No tissue
data were collected upstream of the Site because the river conditions transition from marine and estuarine
to a freshwater environment, with different fish and shellfish species.
Table 5. Summary of PCB, Arsenic, cPAH, and Dioxin/Furan Data for Natural Background
Concentrations in Fish and Shellfish Tissue
Species
Natural Background Fish and Shellfish Tissue Data
Detected
Samples /
Total
Samples
Range of
Detected
Concentrations
Mean
95th Percentile
Upper Confidence
Limit on the Mean
(UCL95)
PCBs (fjg/kg ww)
English sole, rock sole, fillet
158/238
1.3-75
11
13
Dungeness crab (edible meat)
17/17
0.43-1.9
0.87
1.1
Dungeness crab (whole body)
15/15
3.0-16
7.1
9.1
Butter clam, geoduck, horse clam, littleneck clam
(whole body)
24/70
0.09-1.4
0.3
0.42
Inorganic arsenic (mg/kg ww)
English sole, fillet
3/12
0.002 -0.004a
0.002
0.0029
Shiner surfperch (whole body)
8/9
0.009a - 0.03
0.017
0.021
Dungeness crab, slender crab (edible meat)
12/12
0.01 -0.04
0.021
0.026
Dungeness crab, slender crab (whole body)
12/12
0.032-0.13
0.075°
0.13
Eastern softshell clams (whole body)b
6/0
0.047/0.112
0.064
0.087
cPAH TEQ (jjg/kg ww)
Starry flounder, fillet
0/1
<0.11°
<0.11°
NC
Dungeness crab (edible meat)
0/8
< 1.6°
<0.41°
NC
Dungeness crab (whole body)
0/7
< 0.92°
<0.23°
NC
Butter clam, geoduck, littleneck clam (whole body)
3/11
0.069-0.17
0.088
0.12
Dioxin/furan TEQ (ng/kg ww)
Starry flounder, rock sole, fillet
4/4
0.17-0.92
0.42
NC
Dungeness crab (edible meat)
27/27
0.027- 1.4
0.24
0.53
Dungeness crab (whole body)
25/25
0.089-5.1
0.81
2.0
Butter clam, geoduck, horse clam, littleneck clam
(whole body)
43/43
0.011-1.6
0.34d
0.71
NC - cannot be calculated
a. This value is an analytical estimate.
b. Only clams collected from Dungeness Spit were selected by EPA for this category, as these were the only ones in the
dataset likely unaffected by the atmospheric deposition of arsenic from the former Tacoma ASARCO smelter.
c. There were no detected values in this category.
d. This is a nonparametric mean, as there was no discernible distribution according to ProLICL v. 4.1
28
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Proposed Plan — Lower Duwamish Waterway Superfund Site
4 Summary of Site Risks
As a standard part of the RI/FS, human health and ecological risk assessments (HHRA and ERA) were
conducted to determine potential pathways by which people (human receptors) or animals (ecological
receptors) could be exposed to contamination in seafood, sediments, or water, the amount of
contamination receptors of concern may be exposed to, and the toxicity of those contaminants. Multiple
exposure pathways by which humans or animals could be exposed to contaminants in the in-waterway
portion of the Site (referred to as the "waterway" or LDW) were evaluated.
4.1 Human Health Risks
As part of the RI, a baseline HHRA was conducted to estimate the risks and hazards to human health
associated with current and potential future exposures to contamination in the waterway. A four-step
process was used as described in "What is Human Health Risk and How is it Calculated?" on the next
page. First, EPA identified contaminants of potential concern that were detected in sediments, fish, and
shellfish in the LDW at concentrations that exceeded risk-based screening criteria. EPA then identified
exposure scenarios for evaluation in the HHRA, as shown in Figure 6 and described below:
Consumption of resident seafood from the LDW - Risks were evaluated for Tribal members (adults
and children), Asian and Pacific Islanders (adults), and other consumers (adults).
Direct contact with sediment - Risks were evaluated for exposure to contaminated sediment through
both dermal (skin) contact and incidental ingestion during commercial netfishing (adults), clamming
(adult Tribal members and recreational users), and beach play (children).
The LDW HHRA relied on an analysis of LDW and Elliott Bay swimming risks evaluated by King
County in 1999 for risks due to exposure to contaminants in surface water while swimming. The excess
lifetime cancer risks (excess cancer risks) for swimming were determined to be less than 1 in 1,000,000,
lower than any other risk evaluated for the waterway. Because of these low risks, the swimming pathway
was not evaluated further in the HHRA.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
What is Human Health Risk, and How is it Calculated?
A Superfund human health risk assessment estimates the "baseline risk." This is an estimate of the likelihood of health problems occurring
if no cleanup action were taken at a site. To estimate the baseline risk at a Superfund site, EPA undertakes a four-step process:
• Stepl: Analyze Contamination Data
Step 2: Estimate Exposure
Step 3: Assess Potential Health Dangers
Step 4: Characterize Site Risk
In Stepl, EPA gathers and analyzes data on the concentrations of contaminants found at a site to identify the contaminants that will be the
focus of the risk assessment.
in Step 2, EPA considers the different ways that people might be exposed to the contaminants identified in Step 1, the concentrations that
people might be exposed to, and other information needed to determine the amount of a contaminant that could enter a person's body, such
as how frequently they might be exposed to the contamination. Using this information, EPA calculates a "reasonable maximum exposure"
(RME) scenario, Vv'hich portrays the highest level of human exposure that could reasonably be expected to occur.
In Step 3, EPA collects information on cancer risk and non-cancer toxicity of each contaminant of potential concern using past scientific
studies on the effects of these contaminants on people or animals.
In Step 4, EPA uses the information from the three previous steps to determine whether site cancer or non-cancer risks are great enough to
potentially cause health problems for people at or near the Superfund site. EPA risk estimates are designed to err on the side of protecting
the public. The likelihood of any kind of cancer resulting from exposure to contaminants at a Superfund site is generally expressed as a
probability; for example, a "1 in 10,000 chance" of developing cancer over the course of a lifetime. In other words, for every 10,000 people
that could be exposed, one extra cancer may occur as a result of exposure to site contaminants. An extra cancer case means that one more
person could get cancer than would normally be expected to from all other causes.
For non-cancer health effects, EPA calculates a "hazard quotient" (HQ). The hazard quotient is the dose of a contaminant a person might be
exposed to divided by a risk-based threshold level. If the ratio is 1 or less, no non-cancer effects are expected for individual chemicals.
A "hazard index" (HI) considers the non-cancer effects of multiple contaminants using the same approach.
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~
E
K
¦
¦
~
~
(3
¦
•><•!• water
biota (food)
sediment
| complete and quantified
] complete; not quantified because of low exposure potential
^ incomplete 1
Figure 6. Conceptual Model for Baseline Human Health Risk Assessment
30
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Reasonable maximum exposure (RME) scenarios represent the highest exposures that are reasonably
expected to occur at a site. Consistent with EPA's Human Health Risk Assessment policy and the
findings of the EJ Analysis (Appendix B), the HHRA evaluated RME excess cancer risk and non-cancer
hazards for children, low income, minority, and Tribal communities. People in the following groups eat
more fish and shellfish on average than the general population: Tribal adults, Tribal children, and
Asian/Pacific Islander adults. The consumption rates used for RME scenarios ranged from 2 to 13 eight-
ounce meals per month. Meals consisted of a combination of fish (English sole or other flatfish and perch)
and shellfish (crabs, clams, and mussels) based on information from regional seafood consumption
surveys of Native Americans and Asian/Pacific Islanders. Although salmon are a highly preferred and
consumed fish from the LDW, human health risks were not calculated for the consumption of salmon
because most of the contaminants in their bodies are accumulated while they are feeding in the open
ocean, where they spend most of their lives. Central tendency or average risks were also estimated for
these groups. Additionally, an upper bound Tribal risk estimate was derived using estimated Tribal
consumption rates based on Suquamish Tribe seafood consumption data. Finally, the risk assessment
provided information that individuals could use to assess the risks that would result from consuming one
meal per month of different species found in the LDW.
For evaluation of risk related to direct contact exposure to contaminated sediment, each exposure scenario
evaluated dermal (skin) contact and incidental ingestion pathways. Commercial netfishers may come into
contact with sediments anywhere in the LDW. The risk assessment focused on clam habitat areas
accessible by boat or shore to evaluate clamming risks, while children's beach play activities were
evaluated over several discrete areas of intertidal sediment accessible from the shoreline, assuming that
small children would not access all intertidal sediments. Figure 2 shows the areas used for the clamming
and beach play scenarios.
PCBs, arsenic, cPAHs and dioxins/furans were identified as human health COCs based on an excess
cancer risk greater than 1 in 1,000,000 for carcinogenic chemicals, or a hazard quotient (HQ) greater than
1 for non carcinogens. For any given contaminant, the HQ is the ratio of the exposure concentration or
dose to the lowest observed adverse effect level; the hazard index (HI) is the same but for multiple
contaminants. Although BEHP, pentachlorophenol, vanadium, tributyltin, and several pesticides were
found in the waterway at concentrations that exceeded risk thresholds, they were not selected as COCs
due to low detection frequency, low contribution to overall risk, or quality assurance concerns with
analytical data.
Table 6 provides a summary of the risk levels associated with each COC and exposure scenario.
31
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Table 6. Cancer and Non-Cancer Risk Estimates for Human Health Scenarios
RME Scenario3
Medium
Contaminant of
Concern
Excess Cancer Risk
Hazard
Quotient
PCBs
2
n 1,000
40
Adult Tribal Seafood
Fish and
Inorganic arsenic
cPAHs
Other
Total
2
O
n 1,000
n 100,000
n 1,000
n 1,000
4
< 1
3.6
Consumption - Tulalip Survey
Shellfish
0
4
4
PCBs
3
n 10,000
87
Child Tribal Seafood
Fish and
Inorganic arsenic
cPAHs
Other
Total
3
O
n 10,000
n 100,000
n 100,000
n 10,000
8
< 1
6.4
Consumption - Tulalip Survey
Shellfish
0
8
8
PCBs
5
n 10,000
29
Adult Asian Pacific Islander
Fish and
Inorganic arsenic
cPAHs
Other
Total
7
q
n 10,000
n 100,000
n 10,000
n 1,000
3
< 1
2.3
Seafood Consumption
Shellfish
0
1
1
PCBs
2 in 1,000,000
< 1
Arsenic
6 in 1,000,000
< 1
Netfishing (Direct Sediment
Subtidal and
Intertidal
Sediment
cPAHs
1 in 1,000,000
< 1
Contact)
Dioxins/Furans
2 in 100,000
< 1
Other
2 in 1,000,000
< 1
Total
3 in 100,000
-
PCBs
8 in 1,000,000
< 1
Arsenic
2 in 100,000
< 1
Clamming (Direct Sediment
Intertidal
cPAHs
5 in 1,000,000
< 1
Contact)
Sediment
Dioxins/Furans
1 in 10,000
< 1
Other
6 in 1,000,000
< 1
Total
1 in 10,000
-
PCBs
3 in 100,000,000 to
6 in 100,000
< 1b
Arsenic
3 in 1,000,000 to
Beach Play (Direct Sediment
Contact-Ranges for 8
beaches)
Intertidal
Sediment
cPAHs
Dioxins/Furans
Total
3 in 100,000
1 in 1,000,000 to
8 in 1,000,000
1 in 10,000,000 to
1 in 100,000
4 in 1,000,000 to
6 in 10,000
< 1
< 1
< 1
a. For the netfishing and clamming RME scenarios, the total excess cancer risks are based data from the Remedial
Investigation. For the beach play RME scenarios, the total excess cancer risks include additional data collected during the
Feasibility Study.
b. All beaches but Beach Play Area 4 at RM 2.2 have HQ <1. The Beach Play Area 4 HQ of 2 excludes two very high PCB
concentrations (see footnote b to Table 1); If the two high PCB concentrations were included, the HQ would be 187. Beach
Play Areas are shown in Figure 2.
32
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Dioxins and furans are not included in the total excess cancer risk calculation for the RME seafood
consumption scenarios because dioxin/furan seafood tissue data were not collected during the RI. These
data were not gathered during the RI because data already available indicated that dioxin/furan
concentrations in most Puget Sound fish and shellfish would present unacceptable risk at the RME
consumption rates; therefore additional data were not needed and the HHRA assumed unacceptable risks
due to dioxins/furans in the LDW without further investigation. However, in May 2007, after the HHRA
was finalized, Ecology sampled and analyzed a few skin-off English sole fillets collected near Kellogg
Island. The excess cancer risks associated with dioxins/furans were calculated to be 6 in 100,000 for the
Adult Tribal RME scenario. However, this risk estimate is uncertain because it is based on a smaller
number of samples than in datasets typically used for an HHRA and is from a very limited portion of the
LDW. It also does not include dioxin concentrations for all seafood species used in the HHRA.
Nevertheless, it provides some information on dioxin/furan risks relative to other COCs.
Figure 7 summarizes the baseline (before cleanup) excess cancer risk and the non-cancer risk related to
the number and type of seafood meals consumed per month. Figure 8 and Figure 9 summarize the excess
cancer risk and the non-cancer risk associated with the RME scenarios for seafood consumption and
direct sediment contact, respectively. Site seafood consumption RME risks exceed direct contact risks,
seafood consumption risks RME and direct contact HQs exceed risk thresholds established by CERCLA,
which are excess cancer risks of 1 in 10,000, and the non-cancer HQ (or HI) of 1. MTCA thresholds are
also exceeded, which are excess cancer risks of 1 in 1,000,000 for individual contaminants or 1 in
100,000 for multiple contaminants, and the non-cancer HQ or HI of 1. Direct contact HQs were less than
1, with the exception of beach play at Beach Area 4 (Table 6).
The COCs associated with the highest risks varied for direct contact and seafood consumption exposures.
The majority of risks for seafood consumption were from PCBs and inorganic arsenic. While risks from
PCBs were associated with all types of fish and shellfish evaluated, the vast majority of risks due to
inorganic arsenic and cPAHs (96-98%) were attributable to consumption of clams. The majority of risks
for adult direct sediment exposure pathways were from dioxins and furans. In contrast, the majority of
risks for children through direct sediment exposure pathways (i.e., beach play) were from cPAHs, because
cPAHs are more toxic to young children than to adults.
PCBs, arsenic, cPAHs, and dioxins/furans, along with the COCs identified by the Ecological Risk
Assessment, were used to identify areas requiring cleanup in the FS. Other contaminants that exceeded
risk thresholds but were not designated as COCs were still evaluated in the FS to ensure that a cleanup
based on the COCs would also address risk due to these other contaminants.
33
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Proposed Plan — Lower Duwamish Waterway Superfund Site
1 in 100
lin
10,000,000
English sole (fillet)
;iCrab (edible meat)
Crab (whole body)
a Clams
Perch (whole body)
The shaded area indicates EPA's acceptable lifetime excess cancer
risk range under CERCLA. The dotted line indicates the
MTCA threshold for the sum of multiple carcinogens.
1 meal every
other month
1 mea
per month
1 meal
per week
3 meals
per week*
« 100
CO
u
a.
y
c
o
<3
CD
¦ English sole (fillet)
¦ Crab (edible meat)
Crab (whole body)
¦ Clams
Perch (whole body)
The dotted line indicates the non-cancer
HQ threshold of 1, which is applicable under
both CERCLA and MTCA guidance
1 meal every
other month
1 meal
per month
1 meal
per week
3 meals
per week*
* 3 meals per week is approximately equal to the rate used for the adult tribal RME seafood consumption rate. One meal is
equal to 8 ounces.
Baseline lifetime excess cancer risks are calculated as the sum of the risk estimates for inorganic arsenic, cPAHs, and PCBs.
These estimates do not include risk estimates from dioxins and furans, as discussed in Section 4.1.
Baseline HQs: HQs are presented for PCBs only because non-cancer HQs were by far the highest for PCBs.
Figure 7. Baseline Excess Cancer Risk and Non-Cancer Hazard Quotients for Consumption of
Various Seafood Species as a Function of the Number of Meals Consumed per Month
34
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Proposed Plan — Lower Duwamish Waterway Superfund Site
90
80
70
S 60
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-------
Proposed Plan — Lower Duwamish Waterway Superfund Site
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o
-------
Proposed Plan — Lower Duwamish Waterway Superfund Site
4.2 Ecological Risks
The baseline Ecological Risk Assessment (ERA) evaluated risks to four types of ecological receptors
exposed to the contaminants in the LDW sediment, either directly or via ingestion of prey: bottom-
dwelling organisms (benthic invertebrates), crabs, fish (juvenile Chinook salmon, Pacific staghorn
sculpin, English sole), and wildlife species (spotted sandpiper, great blue heron, osprey, river otter, and
harbor seal). These species were selected to represent organisms with a range of characteristics that affect
exposure, such as habitat, dietary preferences, level in the food chain, sensitivity to contaminants, and
status as a threatened or endangered species. Generally, if these particular species are protected then the
many species they represent are also protected. Like the HHRA, this was a baseline risk assessment, an
estimate of the likelihood of ecological problems occurring if no cleanup action is taken. Summaries of
exposure pathways determined to be complete for ecological receptors are provided in Figure 10 and
Figure 11.
The baseline ERA concluded the following:
Risks to bottom-dwelling organisms (benthic invertebrates) - Effects on the benthic invertebrate
community were assessed by comparing the contaminant concentrations in LDW surface sediment and
results of site-specific toxicity tests to the SMS standards (see What are the Sediment Management
Standards? on this page). Forty-one contaminants were determined to present risks to benthic
invertebrates because their concentrations in surface sediments exceeded the SQS. For any sample that
exceeded the SQS (or CSL) but did not exceed the biological criteria, the sample was designated as not
exceeding the SQS (or CSL). Based on data from the FS, one or more of the SQS (SQS or CSL) were
exceeded in approximately 18%, or 80 acres, of the LDW. In 16 of those 80 acres (4% of the LDW) the
CSL was exceeded, indicating a higher likelihood of adverse effects. The three COCs with the most
frequent exceedances were PCBs, bis(2-ethylhexyl)phthalate (BEHP), and butyl benzyl phthalate. For all
other COCs, exceedances occurred in 5% or less of the sediment samples (Table 7).
What are the Sediment Management Standards (SMS)?
The SMS are State standards designed to reduce and ultimately eliminate adverse effects on biological resources and
significant health threats to humans from surface sediment contamination.
The SMS include two tiers of numerical standards, both based on relationships between sediment contaminant
concentrations and adverse effects on benthic invertebrates (reduced population size or laboratory toxicity tests showing
mortality, reduced growth, or impaired reproduction) using several hundred samples from the Puget Sound area. They are:
tier 1) sediment quality standards (SQS), lower numerical chemical concentrations below which contaminants are designated
as having no adverse effects on benthic invertebrates; and tier 2) cleanup screening levels (CSLs), higher chemical
concentrations at which there is a potential for more pronounced adverse effects on benthic invertebrates. The sediment
cleanup standards are set as close as practicable to the SQS.
The SMS also provides SQS and CSL biological-effects criteria that allow the use of site-specific toxicity tests and benthic
community abundance data to determine compliance with the SMS instead of basing the determination on the numerical
standards.
The SMS numerical standards do not address risks to people, mammals, birds, and other organisms due to bioaccumulation
of contaminants in the food chain; those risks are addressed through narrative standards.
37
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Risk to crabs, fish, birds and mammals - A hazard quotient (HQ) approach was used to assess risk for
these organisms. The HQ was calculated for fish and crabs by dividing the contaminant concentration in
the organism itself by the respective concentration from the scientific literature that indicated a potential
for adverse effects. For birds and mammals, the HQ was calculated by dividing the contaminant
concentration in items ingested (prey, water and sediments) by the respective concentration from the
scientific literature that indicated a potential for adverse effects. Calculated risk to these organisms was
low, with the exception of river otters. River otters have a higher risk of adverse effects such as reduced
reproductive success from the ingestion of seafood contaminated with PCBs.
Selection of COCs - A subset of COCs were identified as ecological COCs to focus the evaluation of
remedial alternatives for the LDW. Forty-one contaminants (including PCBs) were identified as COCs for
benthic invertebrates, and PCBs were also identified as a COC for river otters (Table 7).
4.3 Basis for Action
It is EPA's judgment that the Preferred Alternative identified in this Proposed Plan, or one of the other
active measures considered in this Proposed Plan, is necessary to protect public health or welfare or the
environment from actual or threatened releases of hazardous substances into the environment.
Table 7. Surface Sediment Contaminant Concentrations and Comparison to SMS Numerical
Standards
Summary Statistics for
Total Number of Surface Sediment
Surface Sediments
Samples that Exceed the SQS or CSLb
Minimum
Maximum
Detected
Detected
Total
> SQS,
> SQS or
Concen-
Concen-
Sam-
Detection
< CSL,
> CSL,
CSL,
Contaminant
tration
tration
Mean
ples
Frequency
detected
detected
detected
Metals (mg/kg dw)
Arsenic
1.2
1,100
17
918
94%
5
9
14
Cadmium
0.03
120
1.0
895
71%
2
12
14
Chromium
4.8
1,700
41
907
100%
1
10
11
Copper
5
12,000
110
909
100%
0
13
13
Lead
2
23,000
140
909
100%
2
23
25
Mercury
0.015
250
0.53
928
88%
20
30
50
Silver
0.018
270
1.0
876
61%
0
10
10
Zinc
16
9,700
190
906
100%
26
19
45
PAHs (fjg/kg dw)
2-Methylnaphthalene
0.38
3,300
42
884
19%
1
4
5
Acenaphthene
1
5,200
65
893
39%
16
4
20
Anthracene
0.58
10,000
130
893
73%
2
0
2
Benzo(a)anthracene
4.3
8,400
320
893
92%
10
6
16
Benzo(a)pyrene
6.5
7,900
310
888
92%
7
5
12
Benzo(g,h,i)perylene
2.4
3,800
160
893
86%
10
12
22
38
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Summary Statistics for
Surface Sediments
Total Number of Surface Sediment
Samples that Exceed the SQS or CSLb
Contaminant
Minimum
Detected
Concen-
tration
Maximum
Detected
Concen-
tration
Mean
Total
Sam-
ples
Detection
Frequency
> SQS,
< CSL,
detected
> CSL,
detected
> SQS or
CSL,
detected
Total benzofluoranthenes
6.6
17,000
730
887
94%
6
6
12
Chrysene
5
7,700
470
893
95%
29
3
32
Dibenzo(a,h)anthrecene
1.6
1,500
62
893
56%
18
6
24
Dibenzofuran
1
4,200
54
890
31%
7
3
10
Fluoranthene
11
24,000
890
893
97%
35
12
47
Fluorene
0.68
6,800
78
893
48%
11
3
14
lndeno(1,2,3-cd)pyrene
5.2
4,300
180
893
90%
16
13
29
Naphthalene
3
5,300
49
884
21%
0
2
2
Phenanthrene
4.1
28,000
430
893
93%
27
3
30
Pyrene
8.3
16,000
720
893
96%
2
6
8
Total HPAH
20
85,000
3,800
893
98%
25
6
31
Total LPAH
4.7
44,000
700
893
94%
4
3
7
Phthalates (iug/kg dw)
Bis(2-ethylhexyl) phthalate
5.4
17,000
590
887
79%
46
58
104
Butyl benzyl phthalate
2
7,100
87
879
54%
80
10
90
Dimethyl phthalate
2
440
25
879
21%
0
2
2
Chlorobenzenes (iug/kg dw)
1,2,4-Trichlorobenzene
1.6
940
19
872
1%
0
2
2
1,2-Dichlorobenzene
1.3
670
19
872
2%
0
4
4
1,4-Dichlorobenzene
1.5
1,600
23
872
6%
0
4
4
Hexachlorobenzene
0.4
95
17
875
5%
4
2
6
Other SVOCs and COCs (iug/kg dw)
2,4-Dimethylphenol
6.1
290
44
870
3%
0
25
25
4-Methylphenol
4.8
4,600
43
887
13%
0
4
4
Benzoic acid
54
4,500
240
877
13%
0
9
9
Benzyl alcohol
8.2
670
49
868
4%
9
7
16
n-Nitrosodiphenylamine
6.5
230
27
872
3%
0
2
2
Pentachlorophenol
7
14,000
120
841
4%
1
1
2
Phenol
10
2,800
91
887
32%
19
6
25
PCBs (yg/kg dw)
PCBs
19
220,000a |
1,100
1393
94%
336
179
515
NOTE: Based on FS baseline dataset.
a Two PCB samples, at the Inlet at RM 2.2, were considered outliers and were not included in the data considered; their
detected concentrations were 230,000 and 2,900,000 pg/kg.
b. As required by the SMS and described in the RI/FS Reports, for some organic compounds, dry weight values shown in this
table were normalized to organic carbon (OC) for comparison to SQS and CSL (see Table 9).
39
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Proposed Plan — Lower Duwamish Waterway Superfund Site
water
biota (food)
sediment
complete and significant
I | complete and significance unknown
~ complete and insignificant
^ incomplete
Pathways
Receptors of Concern
c
2
u
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c
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Figure 10. Conceptual Site Model for LDW Fish and the Benthic Invertebrate Community
Surface
Water
Surface
Water
Sources
T
Sediment
3
T
Biota
_L
Groundwater
water
biota (food)
sediment
Receptors
of Concern
Heron
Osprey
Sandpiper
River Otter
Harbor Seal
I | complete and significant
~ complete and significance unknown
] complete and insignificant
incomplete
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8 .a |
| I §
= £ fc
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Figure 11. Conceptual Site Model for Wildlife
40
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Proposed Plan — Lower Duwamish Waterway Superfund Site
5 Scope and Role of the Response Action
Given the need for CERCLA action, EPA is proposing to select an LDW in-waterway remedy as the third
and final part of an overall strategy for addressing contamination in the waterway and surrounding
watershed that includes: 1) early identification and cleanup of EAAs to address the most contaminated areas
in the waterway; 2) controlling sources of contamination to the waterway; and 3) cleanup of the remaining
contamination in the waterway, including long-term monitoring to assess the success of the remedy in
achieving cleanup goals. These three components together are designed to address the areal extent of
contamination at the Site, including resident seafood tissue concentrations and water quality within the
waterway, to the fullest practicable extent. As described below, the Preferred Alternative (this proposed
action) is intended to be the final remedy for the in-waterway portion of the Site, to be implemented after
completion of additional sampling during the design phase of remedy implementation (remedial design),
and after implementation of the EAA cleanups and sufficient source control to minimize recontamination.
5.1 Component 1: Early Identification and Cleanup of EAAs
The first phase of the LDW RI included identification of the most contaminated areas of the waterway for
consideration as EAAs. Section 2.1 describes progress to date on cleaning up the EAAs. Cleanup
alternatives, costs, and outcomes in this Proposed Plan assume completion of the EAA cleanups, all of
which are scheduled for implementation by the end of 2015.
EPA has reviewed the EAA cleanup actions being performed under EPA Consent Orders and has
determined that the completed Slip 4 EAA is consistent with the Preferred Alternative and requires no
further active remediation, and other planned EAAs are similarly expected to require no further active
remediation if they achieve their stated objectives. Nevertheless, as with the rest of the LDW, all the EAAs
will be subject to performance review to assure that human health and the environment are being protected.
EPA will review the Institutional Controls Plans and long-term monitoring plans for all EAAs and will
require that the EAAs be incorporated into plans for the rest of the LDW as necessary to make them
consistent with the selected remedy in the ROD. For the cleanups conducted under the 1991 Natural
Resource Damages Consent Decree (Duwamish/Diagonal CSO/SD and Norfolk CSO), EPA will conduct a
review during the remedial design phase to determine whether any additional work is needed to make these
cleanup actions consistent with the selected remedy in the ROD.
5.2 Component 2: Controlling Sources of Contamination
As a general principle, EPA seeks to control sources of contamination early when managing contaminated
sediment risks at hazardous waste sites. Sources of contaminants in LDW surface water and sediments
include combined sewer overflows, stormwater carrying the contaminants of concern via stormwater drains
and other discharges; upland facilities or source areas with contaminants discharging to the LDW via
groundwater, surface water, or erosion of contaminated soils; and atmospheric deposition of COCs. Section
2.2 and Appendix A provide more information on how Ecology as the lead agency for source control is
leading this important component of the Site remediation.
An objective of source control is to find and sufficiently control sources prior to sediment remediation and
thereby prevent or minimize recontamination after the cleanup is completed. EPA and Ecology will
coordinate to sufficiently control ongoing sources to the extent possible before initiating sediment cleanup
41
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Proposed Plan — Lower Duwamish Waterway Superfund Site
in a specific area. The coordination of the source control and sediment cleanup activities will be established
in a Memorandum of Understanding (MOU) to be developed by EPA and Ecology prior to issuance of the
ROD. The MOU will detail how EPA and Ecology will coordinate sequencing of source control and
sediment remedial actions. The process for determining when source control is sufficient to begin sediment
cleanup activities for a particular area without significant risk of recontamination is described in Ecology's
Source Control Strategy in Appendix A.
To date, Ecology and the Source Control Workgroup have performed extensive investigations and initiated
multiple actions to address known sources of contaminants. For a summary of these actions, see Section 2.2
and for more detailed information, see Ecology's website at
http://www.ecy.wa.gov/programs/tcp/sites_brochure/lower_duwamish/lower_duwamish_hp.html.
Appendix A to this Proposed Plan is Ecology's 2012 draft final revision of its 2004 Source Control Strategy.
It provides a broad framework for organizing the work of the federal, state, and local agencies under various
legal authorities. Ecology is separately seeking public comments on this proposed revision, and will provide
responses after EPA's public comment period for this Proposed Plan.
The 2012 Source Control Strategy anticipates a "Source Control Implementation Plan" from each of the
Federal, State, and local source control agencies. The Implementation Plans will describe how each agency
will conduct its various programs to address source control work for the LDW source area. Ecology is
currently requesting implementation plans from EPA, King County and the City of Seattle, and may request
implementation plans from other entities in the future. Ecology will also develop its own Source Control
Implementation Plan. Once completed, these plans will be appended to the Strategy and available on
Ecology's web site. In the unlikely event that timely and effective source control is not implemented, EPA
may implement actions pursuant to CERCLA or other Federal authority to ensure the protectiveness of the
remedy selected in the ROD following public comment on this Proposed Plan.
5.3 Component 3: In-Waterway Cleanup
The third element of the overall cleanup strategy for the Site, and the focus of this Proposed Plan, is the in-
waterway cleanup. The alternatives considered in this Proposed Plan, including the Preferred Alternative,
address contaminated sediments and surface water below the mean higher high water (MHHW) level (11.3
feet above the mean lower low water level [MLLW]) that are expected to remain after completion of the
EAA cleanup work (component 1). Although no alternatives directly address surface water, COC
concentrations in surface water will be reduced through implementation of source control and sediment
cleanup. The proposed cleanup will be implemented after completion of additional sampling and remedial
design, and implementation of the EAA cleanups (component 1) and sufficient source control (component
2) to minimize recontamination in any particular area within the waterway.
The Preferred Alternative described in this Proposed Plan is a final action which will be protective of public
health and the environment, as described in detail in Section 10. It is EPA's expectation that once all
anticipated action for the Site has been implemented, COC concentrations in the sediment, surface water,
and fish and shellfish tissue will be protective of all anticipated uses. These actions include source control
and institutional controls, as necessary, to limit fish and shellfish consumption.
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6 Remedial Action Objectives
In accordance with the NCP, EPA developed Remedial Action Objectives (RAOs) to describe what the
proposed cleanup is expected to accomplish to protect human health and the environment. The RAOs for
the LDW are based on results of the human health and ecological risk assessments described in Section 4.
RAOs help focus the development and evaluation of remedial alternatives and form the basis for
establishing Preliminary Remediation Goals (PRGs) and the cleanup levels to be established in the ROD.
The following four RAOs were established for LDW:
RAO 1: Reduce to protective levels human health risks associated with the consumption of
contaminated resident LDW fish and shellfish by adults and children with the highest potential
exposure. Risk will be reduced by reducing sediment and surface water concentrations or bioavailability
of PCBs, arsenic, cPAHs and dioxins/furans, the primary COCs that contribute to the estimated cancer
and non-cancer risks from consumption of resident seafood, with additional reduction in exposure through
the use of seafood consumption advisories and education and outreach programs as may be needed.
RAO 2: Reduce to protective levels human health risks from direct contact (skin contact and
incidental ingestion) to contaminated sediments during netfishing, clamming, and beach play. Risks
will be reduced by reducing sediment concentrations or bioavailability of PCBs, arsenic, cPAHs, and
dioxins/furans, the primary COCs that contribute to the estimated excess cancer and non-cancer risks.
RAO 3: Reduce to protective levels risks to benthic invertebrates from exposure to contaminated
sediments. Risks will be reduced by reducing sediment concentrations of the 41 contaminants listed in
Table 9 to the chemical or biological SQS.
RAO 4: Reduce to protective levels risks to crabs, fish, birds, and mammals from exposure to
contaminated sediment, surface water, and prey. Risks will be reduced by reducing sediment and
surface water PCB concentrations or bioavailability. Addressing risks to river otters due to consumption
of PCB-contaminated seafood, along with addressing risks associated with RAOs 1-3, will also protect
other ecological receptors.
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7 Preliminary Remediation Goals
This section describes Preliminary Remediation Goals (PRGs) for the in-waterway cleanup. PRGs are
contaminant concentrations used in the FS to measure the success of the cleanup alternatives in meeting
the RAOs. They are based on applicable or relevant and appropriate requirements (ARARs), which
provide minimum legal standards, and other information such as toxicity information from the HHRA and
ERA to address risks that the ARARs do not adequately address. PRGs are refined into final
contaminant-specific cleanup levels in the ROD. EPA proposes to select the PRGs for sediment, surface
water, and fish and shellfish described below as cleanup levels in the ROD, subject to consideration of
public comment.
The most significant ARARs for the in-waterway portion of the Site are in MTCA, which includes the
SMS and its numerical standards for the protection of benthic invertebrates, and the requirements for
protection of human health discussed below. PRGs associated with RAO 3 (protection of benthic
invertebrates) are based on the SQS of the SMS. Consistent with the NCP and as required by MTCA for
final cleanups (WAC 173-340-700(5)(b), (6)(d); 705(2), (4)-(6)), sediment PRGs for RAOs 1 and 2
(protection of human health) were set at a risk-based threshold concentration (RBTC) of 1 in 1,000,000
excess cancer risk, and a non-cancer HQ of 1. Consistent with EPA policy and as required by the MTCA,
where this concentration is more stringent than the background levels, the PRG was set at the MTCA
natural background level (see Section 3.6).
Sediment, fish and shellfish tissue, and surface water PRGs are discussed below. Although fish and
shellfish tissue and surface water are not being directly remediated, they are key exposure pathways that
are being addressed by the Preferred Alternative as part of the areal extent of contamination in the
waterway. For this reason, EPA has determined that it is important to establish PRGs (and cleanup
levels) for them to ensure protectiveness and measure progress towards achieving RAOs. Controlling
sources of contamination to the LDW along with remediation of contaminated sediments will reduce
COC concentrations in surface water and fish and shellfish tissue in addition to reducing COC
concentrations in sediment.
7.1 Sediment PRGs
Table 8 lists sediment PRGs for RAOs 1, 2, and 4, and Table 9 lists sediment PRGs for RAO 3. Sediment
PRGs are either applied to all locations (i.e., point-based; applicable to any sample location) or are
applied over a specific area. Of the four human health COCs, PCBs are the most widespread, and largely
define the cleanup footprint. The exposure areas identified in the risk assessments determine whether a
PRG is applied to the entire LDW, or to a specific exposure area such as a beach. Benthic PRGs (the SQS
numerical standards) can be overridden by biological criteria (see What are the SMS? on page 37) unless
they are collocated with exceedances of human health PRGs. In that case, the human health PRGs are
used to measure compliance.
EPA will determine if PRGs have been met in specific areas of compliance after the cleanup is
completed, including natural recovery. For RAO 3, PRGs must be met at every sampling location. For
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RAOs 1, 2 and 4, the 95% upper confidence limit on the mean (UCL95) measured over the following
areas of compliance will be used to measure success in attaining PRGs.
• For RAO 1, PRGs must be met LDW-wide.
• For RAO 2, PRGs are applied as follows:
- For beach play areas, PRGs must be met at individual beaches identified in Figure 2.
- For clamming areas, PRGs must be met across all clamming areas (Figure 2).
- For net-fishing, PRGs must be met LDW-wide.
• For RAO 4, PRGs must be met LDW-wide.
The PRGs must be met, on average, at varying depths, as described below:
• In intertidal areas including beaches used for recreation and clamming, human-health direct contact
PRGs (for PCBs, arsenic, cPAHs, and dioxins/furans) must be met in the top 45 cm because exposure
to sediments at depth is more likely through digging or other disturbances. Human health PRGs for
RAO 1 (seafood consumption) and ecological PRGs must be met in surface sediments (top 10 cm).
• In subtidal areas, PRGs for all COCs must be met in surface sediments (top 10 cm).
Table 8, Sediment PRGs for PCBs, Arsenic, cPAHs, and Dioxins/Furans for Human Health and
Ecological COCs
coc
Preliminary Remediation Goals
RAO 1:
Human Seafood
Consumption
RAO 2:
Human Direct
Contact
RAO 4:
Ecological
(River Otter)
Basis
Spatial Scale of
PRG Application
PCBs
(Mg/kg dw)
2
1,300
128-159
background (RAO 1)
RBTC (RAO 2)
RBTC (RAO 4)
LDW-wide
n/a
500
n/a
RBTC
Clamming Areas
n/a
1,700
n/a
RBTC
Individual Beaches
Arsenic
(mg/kg dw)
n/a
7
n/a
background
LDW-wide
n/a
7
n/a
background
Clamming Areas
n/a
7
n/a
background
Individual Beaches
cPAH
(|jg TEQ/kg dw)
n/a
380
n/a
RBTC
LDW-wide
n/a
150
n/a
RBTC
Clamming Areas
n/a
90
n/a
RBTC
Individual Beaches
Dioxins/Furans
(ng TEQ/kg dw)
2
37
n/a
background (RAO 1)
RBTC (RAO 2)
LDW-wide
n/a
13
n/a
RBTC
Clamming Areas
n/a
28
n/a
RBTC
Individual Beaches
RBTC - Risk-based threshold concentration (based on 1 in 1,000,000 excess cancer risk or HQ of 1)
Background - see Table 3 in Section 3.6.1
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No sediment PRGs were identified for arsenic or cPAHs for the human health seafood consumption
pathway (RAO 1). Seafood consumption excess cancer risks for these two COCs were largely attributable
to eating clams. However, data collected during the RI/FS showed little relationship between arsenic or
cPAH concentrations in sediment and concentrations in clam tissue. EPA will define the sediment
cleanup footprint based on other PRGs, then use the clam tissue PRGs (Section 7.2) to measure reduction
in cPAH and arsenic concentrations in clams. EPA is conducting research to study the relationships
between clam tissue and sediment concentrations for arsenic and cPAHs and methods to reduce
concentrations of these contaminants in clams. This research will continue into the remedial design phase.
Table 9. Sediment PRGs for Ecological (Benthic Invertebrate) COCs
Benthic COC
Preliminary
Remediation Goals for
RAO 3
Benthic COC
Preliminary
Remediation Goals for
RAO 3
Value
Basis
Value | Basis
SMS metals, (mg/kg dw)
OC-normaiized SMS Organic Compounds (continued)
(mg/kg OC)
Arsenic
57
SQS
Benzo(g,h,i)perylene
31
SQS
Cadmium
5.1
SQS
Chrysene
110
SQS
Chromium
260
SQS
Dibenz(a,h)anthracene
12
SQS
Copper
390
SQS
lndeno(1,2,3-cd)pyrene
34
SQS
Lead
450
SQS
Fluoranthene
160
SQS
Mercury
0.41
SQS
Fluorene
23
SQS
Silver
6.1
SQS
Naphthalene
99
SQS
Zinc
410
SQS
Phenanthrene
100
SQS
Dry Weight Basis SMS Organic Compounds, (iug/kg dw)
Pyrene
1,000
SQS
4-methylphenol
670
SQS
HPAH
960
SQS
2,4-di methyiphenoi
29
SQS
LPAH
370
SQS
Benzoic acid
650
SQS
Bis(2-ethylhexyl)phthalate
47
SQS
Benzyl alcohol
57
SQS
Butyl benzyl phthalate
4.9
SQS
Pentachlorophenol
360
SQS
Dimethyl phthalate
53
SQS
Phenol
420
SQS
1,2-dichlorobenzene
2.3
SQS
OC-normaiized SMS Organic Compounds, (mg/kg OC)
1,4-dichlorobenzene
3.1
SQS
PCBs
12
SQS
1,2,4-trichlorobenzene
0.81
SQS
Acenaphthene
16
SQS
2-methylnaphthalene
38
SQS
Anthracene
220
SQS
Dibenzofuran
15
SQS
Benzo(a)pyrene
99
SQS
Hexachlorobenzene
0.38
SQS
Benz(a)anthracene
110
SQS
n-Nitrosodiphenylamine
11
SQS
Total benzofluoranthenes
230
SQS
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As discussed above, the sediment PRGs for PCBs and dioxins/fiirans (RAO 1) and for arsenic (RAO 2)
are set at natural background for final cleanups. Modeling conducted during the RI/FS (see Sections 3.4
and 3.6.1) projected that long term LDW COC concentrations would be higher than natural background
regardless which of the cleanup alternatives is selected. This is because the concentrations of these
contaminants in incoming sediments (suspended solids) from the Green/Duwamish River are currently
higher than natural background and because of practical limitations on control of sources within the LDW
and Green/Duwamish River drainage basins.4 The term cleanup objective was used in the FS to mean the
PRG or as close as practicable to the PRG. For the purposes of comparing alternative remedies, the lowest
model-predicted concentration was used as a surrogate for "as close as practicable to the PRG" when the
PRG was not predicted to be achieved within a 45-year period. These long-term model-predicted COC
concentrations are highly uncertain, because future concentrations in upstream and lateral-source
sediments are uncertain. Ecology and King County are currently conducting studies to refine estimates of
contaminant inputs from the Green/Duwamish River, and to better understand upstream sources of
contamination. Ecology in consultation with EPA will use this information to further assess upstream
source control. All predictions of future outcomes in the FS and in this Proposed Plan are based on RI/FS
data, which necessarily do not reflect anticipated refinements in estimates of contaminant loading to the
LDW from upstream, and potential reductions due to future source control in the Green/Duwamish
watershed. EPA is therefore retaining natural background, along with the risk-based values (RBTCs), as
PRGs for LDW sediments.
7.2 Fish and Shellfish Tissue PRGs
EPA has determined that fish and shellfish tissue PRGs (and ultimately cleanup levels) are necessary and
appropriate for this Site because they are the most direct and reliable measure of risk to people consuming
seafood. Fish and shellfish PRGs are not based on ARARs, because MTCA defines a cleanup level as a
"concentration of a hazardous substance in soil, water, air, or sediment" (WAC 173-340-200 and 700(2)).
However, tissue PRGs have been developed consistent with the criteria for developing the sediment PRGs
(which are based on MTCA ARARs) to ensure protectiveness for humans, including sensitive
subpopulations.
Table 10 lists PRGs for resident fish and shellfish (crab and clam) tissue for RAO 1. Tissue PRGs are
based on the higher of: the RBTC at 1 in 1,000,000 excess cancer risk or HQ of 1 for the adult Tribal
RME scenario; or the current concentrations in non-urban Puget Sound data. Fish and crab tissue PRGs
must be met as a 95% UCL LDW-wide. Clam tissue PRGs must be met as a 95% UCL across all
clamming areas.
4. For example, the PCB sediment PRG for seafood consumption is 2 |ig/kg. while the BCM predicts that post-
cleanup PCB concentrations will reach a steady state at approximately 40 ng/kg over 45 years, with a sensitivity
range using low and high input values of approximately 9 - 100 |ig/kg.
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Table 10. LDW Resident Fish and Shellfish Tissue PRGs
Species/Group and Tissue Type
Speciesab
PRG
Source of PRG
PCBs (jjg/kg ww)
Benthic fish, fillet
English sole
12
background
Pelagic fish, whole body
Perch
1.8
RBTC
Crab, edible meat
Dungeness crab
1.1
background
Crab, whole body
Dungeness crab
9.1
background
Clams
Eastern softshell clam
0.42
background
Inorganic arsenic (mg/kg ww)
Clams
Eastern softshell clam
0.09
background
cPAH TEQ fag/kg ww)
Clams
Eastern softshell clam
0.24
RBTC
Dioxin/furan TEQ (ng/kg ww)
Benthic fish, whole body
English sole
0.35
background
Crab, edible meat
Dungeness crab
0.53
background
Crab, whole body
Dungeness crab
2.0
background
Clams
Eastern softshell clam
0.71
background
a Substitutions of similar species may be made if sufficient numbers of the species listed here are not available,
b Background - see Table 5 in Section 3.6.2
As discussed in Section 3.6.2, fish and shellfish tissue PRGs based on background data are uncertain
because they were developed with a limited dataset. Additional fish and shellfish background data will be
collected during the remedial design phase to increase understanding of non-urban tissue concentrations of
the human health COCs. Similar to sediment PRGs, post-cleanup tissue concentrations (for PCBs only)
were predicted in the FS using the BCM and food-web model. These models predict that background-based
fish and shellfish tissue PRGs for PCBs will not be met in the long term because of the influence of
incoming water and suspended sediments from the Green/Duwamish River, as well as incoming surface
water from Elliott Bay. If true, this is likely to be the case for tissue PRGs for other COCs as well. As
discussed in Section 7.1, these model-predicted values are highly uncertain, and EPA is retaining the
background-based values as PRGs. If appropriate, EPA may adjust these PRGs based on new data, which
would be documented in a ROD Amendment or ESD.
7.3 Surface Water PRGs
As discussed above, surface water will not be directly remediated, but it is a key exposure pathway to
aquatic organisms and those that consume them. Therefore, it is important to establish surface water PRGs
(and cleanup levels) and monitor surface water quality to measure progress towards achieving RAOs 1 and
4. The PRG for PCBs in surface water is 0.064 ng/L, based on the recommended Ambient Water Quality
Criteria (AWQC) for the protection of human health for consumption of organisms only. EPA is
establishing this PRG for the Preferred Alternative (Section 10) as a proposed cleanup level for the ROD
based on the water column data that was collected prior to or during the RI/FS. During remedial design
sampling, EPA intends to further evaluate surface water COC concentrations. If other COC surface water
concentrations exceed the recommended Federal AWQC (Clean Water Act Section 304(a) guidance
values) or State Water Quality Standards, the more stringent of the two will be used to monitor progress
towards achieving RAOs.
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8 Development of Remedial Alternatives
Remedial alternatives for the LDW were developed to meet the requirements of CERCLA and its
regulations, the NCP, and MTCA and its regulations (including the SMS). The NCP and MTCA require
that a range of remedial alternatives be evaluated to provide protection of human health and the
environment primarily by preventing or controlling exposure to hazardous substances, pollutants, or
contaminants within a site. The development and analysis of the remedial alternatives form the basis for
EPA's selection of the Preferred Alternative and are discussed below.
8.1 Framework for Developing Remedial Alternatives
EPA considered several factors in developing remedial alternatives, including: the levels of COCs in
surface and subsurface sediments, the likelihood of contact with contaminated sediments, the likelihood
that sediment disturbances, many of which can result from ordinary use of the waterway, might expose
contamination in the future, and the potential for contaminated sediments to be covered by incoming
cleaner sediments and therefore pose less risk. EPA also considered use of the waterway by people and
aquatic organisms, as discussed in Section 8.2. To support the evaluation of alternatives, EPA used three
criteria: 1) Remedial Action Levels (RALs); 2) PRGs (described in Section 7); and 3) Recovery
Categories.
Remedial Action Levels (RALs) are contaminant-specific sediment concentrations that will be used to
identify specific areas of sediments that require active remediation (dredging, capping, enhanced natural
recovery [ENR], or a combination thereof), taking into consideration the human health and ecological risk
reduction that could be achieved by the different remedial technologies. These RALs are set by EPA so
that, in each area, PRGs will be met either immediately after construction or in the long term after natural
recovery, to the extent practicable given the uncertainties discussed in Section 7. The sediment RALs in
this Proposed Plan are equal to or higher than the sediment PRGs for each COC and are used only to
delineate the Site into areas where different remedial technologies would be used. The use and application
of RALs does not affect or alter the requirement to achieve cleanup levels established in the ROD.
A number of alternative cleanup options (alternative remedies) are presented in this Proposed Plan. Each
alternative has its own set of sediment RALs. Sediment RALs reflect a range in risk reduction to be
achieved over time, in the projected rate of natural recovery, and in which remedial technologies are used.
Different RALs were established for surface and subsurface sediments, intertidal and subtidal sediments,
and Recovery Category areas, as discussed below.
Contaminant-specific RALs for surface sediments are compared to contaminant concentrations in the top
10 cm (4 in) of sediments. Consistent with the SMS, the top 10 cm represents the biologically active zone
where most of the benthic invertebrates reside. For subsurface sediments in intertidal areas (shallower
than -4 ft MLLW), certain RALs (identified as intertidal RALs in Table 12, page 60) are also compared to
the contaminant concentration averaged over the top 45 cm (1.5 ft). For subsurface sediments in
intertidal and subtidal areas with a higher potential for erosion or scour (see Recovery Category 1
description below), RALs are also compared to the contaminant concentration averaged over the top 60
cm (2 ft). Where concentrations exceed the RALs, active remediation technologies are selected based on
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Proposed Plan — Lower Duwamish Waterway Superfund Site
technology assignment criteria described in Section 8.2. Although RALs are applied as an average over
the depth intervals described above, they are applied at each sampling location, not as averaged values
over an area. While RALs were used in the FS to identify areas of active remediation for each alternative,
those areas will be further defined through sampling conducted during remedial design to determine the
areal and vertical extent of sediments to be remediated following cleanup of the EAAs.
PRGs are described in Section 7. In the FS, the projected short-term and long-term sediment and seafood
tissue concentrations after implementation of each alternative (developed using the RALs and Recovery
Categories) were compared to PRGs to measure its protectiveness and compliance with ARARs.
Recovery Categories were used to assign remedial technologies to specific areas based on information
about the potential for sediment contaminant concentrations to be reduced through natural recovery or for
subsurface contamination to be exposed at the surface due to erosion or scour. Based on data collected
and modeling performed in the RI/FS, three Recovery Categories were developed as shown in Table 11.
Table 11. Criteria for Assigning Recovery Categories
Criteria
Recovery Categories
Category 1
Recovery Presumed
to be Limited
Category 2
Recovery Less Certain
Category 3
Predicted to Recover
Physical Criteria
Physical
Conditions
Vessel scour
Observed vessel scour
No observed vessel scour
Berthing areas
Berthing areas with vessel
scour
Berthing areas without
vessel scour
Not in a berthing area
Sediment
Transport
Model
STM-predicted
100-year high-flow
scour (depth in cm)
> 10 cm
< 10 cm
STM-derived net
sedimentation rate
(cm/yr) using
average flow
conditions
Net scour
Net sedimentation
Rules for applying criteria
If an area is in Category 1
for any one criterion, that
area is designated
Category 1
If conditions in an area
meet a mixture of Category
2 and 3 criteria, that area is
designated Category 2
An area is designated
Category 3 only if all
conditions meet the
Category 3 criteria
Empirical Contaminant Trend Criteria - used on a case-by-case basis to adjust recovery categories from the criteria
above
Empirical
Contaminant
Trend
Criteria
Resampled surface
sediment locations
Increasing PCBs or
increasing concentrations
of other detected COCs
exceeding the SQS
(> 50% increase)
Equilibrium and mixed
(increases and decreases)
results (for COCs
exceeding the SQS)
Decreasing
concentrations (> 50%
decrease) or mixed
results (decreases and
equilibrium)
Sediment cores
(top 2 sample
intervals in upper 2 ft)
a Observed vessel scour areas, berthing areas, high-flow scour areas, and modeled net sedimentation rates are shown on
Figure 3.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
The spatial extent of the areas assigned to each of these three categories in the FS is shown in Figure 12.
The use of Recovery Categories allows for more aggressive remedial technologies (such as capping and
dredging) in areas with less potential for natural recovery and a higher likelihood of scour or other
disturbance, and less aggressive remedial technologies (such as ENR and MNR) in areas where recovery
is predicted to occur more readily and disturbance is less likely.
Section 8.2 describes how Recovery Categories are used in assigning cleanup technologies. Recovery
Category areas will be further refined using data collected in the remedial design phase and the criteria set
forth in Table 11.
8.2 Summary of Remedial Alternatives
Using the framework described above, along with other criteria such as maintaining sufficient water
depths for human use and habitat areas, twelve remedial action alternatives were developed in the FS
using varying combinations of technologies as described below. The FS alternatives include one no
further action alternative (Alternative 1), seven removal-emphasis alternatives ("R" Alternatives 2R, 2R-
Contained Aquatic Disposal (CAD), 3R, 4R, 5R, 5R-Treatment, and 6R) and four combined technology
alternatives ("C" Alternatives 3C, 4C, 5C, and 6C). FS Alternative 5C was further modified to include
additional remedial elements as described in a 2012 technical memorandum5 (the FS Supplement), as
discussed in Section 8.2.2; this modified alternative is called 5C Plus in this Plan. A general
approximation of the areas of sediments addressed by the FS cleanup alternatives is shown in Figure 13.
5. Technical Memorandum: Supplement to the Feasibility Study for the LDW Superfund Site, Approaches for
Addressing Additional Concerns in Alternative 5C and Development of Alternative 5C Plus Scenarios for the Lower
Duwamish Waterway (FSSupplement)', see Key Documents.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
River Mile Marker
Navigation Channel
Legend
Recovery Category
ZD
Category 1: Recovery Presumed to be Limited
(77 acres)
Category 2: Recovery Less Certain
(44 acres)
Category 3: Predicted to Recover
(281 acres)
Early Action Area (29 acres)
Outfall Location
Notes:
1 Ten acres of the LDW upstream of RM 4.75 (but not part of EAAs) was
not assigned to one of the three recovery categories because it is upstream of
the area represented by the sediment transport model
Upper
Turning
Figure 12. Recovery Categories
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Legend
Notes:
1. FS study area is 441 acres.
2. The area addressed by the Preferred Alternative (5C Plus) through active remediation
or MNR To SQS (189 acres) is not shown on this figure, but is approximately 9 acres larger
than the area addressed by Alternatives 2 through 5 through active remediation or
MNR (180 acres). The Preferred Alternative has a larger area based on changes to
subsurface sediment remedial action levels
Shoreline Conditions
Armored Slope (10.1 miles)
Exposed Bank (3.7 miles)
Dock Face (4.9 miles)
—— Vertical Bulkhead (1.0 miles)
Road
Navigation Channel
River Mile Marker
i Area Addressed by Alternatives 2-5 (180 acres)
II Area addressed by Alternative 6 (Beyond Alternatives 2-5)
' ' (122 acres)
Early Action Area (EAA, 29 acres)
Rest of LOW Study Area (110 acres)
Y//\ Overwater Structures
Upper
Turning
Basin
Figure 13. Areas Addressed by LDW Cleanup Alternatives
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Proposed Plan — Lower Duwamish Waterway Superfund Site
8.2.1 Technologies Common to all Remedial Alternatives
The remedial cleanup technologies described below were used to develop remedial action alternatives to
address contamination in the LDW, including dredging and excavation, capping, treatment, enhanced
natural recovery (ENR), and monitored natural recovery (MNR). The "no action" alternative would use
no remedial technologies (although it does include long-term monitoring). All alternatives would be
implemented after cleanup is completed in the Early Action Areas (29 acres) along with sufficient source
control to minimize recontamination. The engineered remedial technologies are as follows:
• Dredging and Excavation - Removal of sediments through dredging or excavation in areas where it
is necessary to maintain water depth for human use or to maintain habitat; dredging and excavation is
incorporated into all remedial alternatives.
• Sediment disposal - All alternatives include disposal of dredged or excavated materials at an off-site
upland permitted facility. Alternative 2R-CAD also includes disposal of contaminated sediments in a
contained aquatic disposal (CAD) site within the LDW. Alternative 5R-Treatment includes treatment
of dredged sediments prior to disposal.
• Capping - Many alternatives include capping of contaminated sediments in areas where there is
sufficient water depth to build a cap. Engineered sediment caps are constructed by placing clean sand,
gravel, and rock on contaminated sediments to provide physical and chemical isolation of
contaminants. Caps will be a minimum of 4 feet thick in intertidal clamming areas, and cap thickness
in other areas will be determined during remedial design. In habitat areas, the uppermost layers of
caps will be designed using suitable habitat materials. Other materials, such as activated carbon or
other contaminant-sequestering agents, may be used to reduce the potential for contaminants to
migrate through the cap. The effectiveness and potential impacts of these amendment technologies
will be evaluated in pilot studies performed during remedial design.
• Enhanced Natural Recovery (ENR) - Many alternatives include Enhanced Natural Recovery of
contaminated sediments. ENR refers to the placement of a thin layer (approximately 6 to 9 inches) of
clean sand or other suitable habitat materials on sediments, which immediately provides a new
surface substrate of clean sediments. This cleaner material mixes with the underlying contaminated
material, through mechanisms such as bioturbation. ENR reduces contaminant concentrations in
surface sediments more quickly than would happen by natural sedimentation processes alone. ENR is
proposed for areas with less sediment contamination and only in Recovery Category 2 and 3 areas. In
some areas, ENR may be combined with in situ treatment; in other words, the sand layer may be
amended with activated carbon or other sequestering agents to reduce the bioavailability of organic
contaminants such as PCBs. The effectiveness and potential impacts of using in situ treatment or
amendment technologies, as well as the areas best suited for these technologies, will be evaluated in
pilot studies performed during remedial design.
Other, non-engineered, technologies common to all alternatives include: monitored natural recovery,
monitoring, and institutional controls, as described below:
• Monitored Natural Recovery (MNR) - Monitored natural recovery relies on natural processes to
reduce ecological and human health risks to acceptable levels, while monitoring recovery of
56
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Proposed Plan — Lower Duwamish Waterway Superfund Site
sediments over time to determine remedy success. Within the LDW, natural burial of contaminants
through sedimentation from upstream is the primary natural recovery mechanism. The sediment
transport model (STM) and bed composition model (BCM), supported by RI/FS data, were used to
estimate reduction of sediment COC concentrations over time through natural recovery.
• Two categories of MNR for the Preferred Alternative Only: MNR To SQS and MNR Below
SQS - Terminology used to describe MNR in this Proposed Plan for the Preferred Alternative differs
from that used in the FS, as follows.
- In the FS the term "MNR" referred only to reduction of COC concentrations through natural
processes until the SQS are reached (i.e., only areas where concentrations are above the SQS;
once SQS are reached, MNR would no longer apply and the area would be designated "long-term
monitoring"). As used in the FS, MNR included more intensive monitoring and additional actions
in any areas where the SQS is not achieved within 10 years after remedial action. Areas where
COC concentrations are below the SQS were designated in the FS as "long-term monitoring"
areas with a lower sampling density, although the FS acknowledged that reduction of COC
concentrations through natural recovery would continue in those areas also.
- In this Proposed Plan (and in the 2012 FS Supplement; see Key Documents), the term "MNR" is
used to describe all areas where reduction of COC concentrations through natural recovery is
predicted to continue after cleanup is complete (i.e., areas where concentrations are above the
SQS and areas where they are below the SQS). For the Preferred Alternative only, the Proposed
Plan further refines MNR, dividing it into two different categories: 1) MNR To SQS, for areas
where MNR would be used to achieve the SQS (PRGs for RAO 3); and 2) MNR Below SQS for
areas where MNR is used to further reduce COC concentrations to the remaining PRGs for RAOs
1, 2, and 4. Use of this terminology is more fully described in Section 10.
• Monitoring - Monitoring includes sampling sediments, surface water, fish and shellfish tissue, and
other media to assess site conditions before, during and after cleanup. All alternatives include
baseline monitoring during the remedial design phase. Monitoring will continue through construction
to assess compliance with construction performance standards, and will continue over the long term
to determine whether technologies are operating as intended and to assess progress toward achieving
the cleanup levels.
• Institutional controls - Because none of the alternatives evaluated in the FS would provide
sufficient risk reductions to allow for unrestricted use of the LDW, all alternatives include use of
Institutional Controls (ICs). It is important to recognize that even if all natural background-based
PRGs were met (keeping in mind that calculated risk-based concentrations are more stringent than
background levels), this would not safely allow for unrestricted use of the LDW (human consumption
of unlimited quantities of resident fish and shellfish). The ICs considered for the LDW include:
- Informational devices, such as seafood consumption advisories, public outreach, and education
to reduce human exposure from consuming contaminated fish and shellfish within the LDW, and
monitoring and notification of waterway users, including use of the state's Environmental
Covenants Registry; and
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Proposed Plan — Lower Duwamish Waterway Superfund Site
- Proprietary controls, such as environmental covenants to protect the integrity of the engineered
features such as sediment caps. They would typically require EPA or Ecology approval prior to
activity that may disturb or encounter contamination that remains in the LDW after cleanup.
Institutional controls will only be relied upon to the minimum extent practicable, consistent with MTCA
institutional control regulations (WAC 173-340-440(6)).
8.2.2 Remedial Alternatives
The alternatives use varying combinations of the technologies listed above. Elements that vary among
alternatives include 1) the extent of the active remediation, 2) the technologies assigned, and 3) the COC
concentrations (RALs) where a technology may be applied.
Each of the twelve remedial alternatives are briefly described below. Higher numbered alternatives must
achieve progressively lower RALs and they have increasingly larger cleanup footprints (e.g., the cleanup
footprint for Alternative 3 is larger than that of Alternative 2).
For the alternatives that emphasize removal (the "R" alternatives ), dredging/excavation and disposal
would be the primary technologies used for active remediation. The combined technology ("C")
alternatives emphasize the use of capping, enhanced natural recovery (ENR), and in situ treatment. They
would use dredging and excavation only where capping and ENR/in situ treatment are not feasible due to
requirements to maintain water depths in habitat areas, the navigation channel, or berthing areas. In the
"C" alternatives, ENR is used only in areas with low scour potential and moderate sediment contaminant
concentrations because underlying sediment contamination is not isolated by this technology. For the FS
and this Proposed Plan, moderate contamination is defined as 1 to 1.5 times the intertidal RAL (applied in
the top 45 cm) and 1 to 3 times the LDW-wide RAL (applied in the top 10 cm). More aggressive
technologies such as isolation caps would be used in highly contaminated areas (where concentrations are
greater than 1.5 times the intertidal RAL or 3 times the LDW-wide RAL) and in areas with scour
potential. Dredging, and partial dredging and capping, would be used where elevation constraints
preclude capping alone.
Figure 13 shows the areas that would be addressed by the cleanup alternatives. The areas addressed by the
cleanup alternatives depicted in the FS and this Proposed Plan are preliminary. The sediment contaminant
concentrations used to delineate the areas addressed in FS remedial alternatives were collected over a 20-
year period, from 1991 to 2010, with the bulk of the data collected prior to 2005. For the final remedy,
different sediment contaminant concentrations may be established based on results from sampling
conducted during remedial design; for example, some areas may have already recovered naturally while
others may have become more contaminated due to ongoing input from contaminant sources. The specific
areas to be addressed by remedial technologies and MNR will be refined based on results from additional
sampling during remedial design.
Because all alternatives use similar technologies, the primary ARARs are the same for all alternatives,
and are described in Section 9. All Alternatives (except Alternative 1, No Action) include off-site disposal
of dredged material. Data from the RI/FS indicate that sediment removed from the LDW can be disposed
of in a solid waste (RCRA Subtitle D) landfill. If wastes that require disposal in a landfill permitted to
58
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Proposed Plan — Lower Duwamish Waterway Superfund Site
receive RCRA hazardous wastes or Toxic Substances Control Act (TSCA) regulated wastes are
encountered during remedial design or remedial action, they will be disposed in a RCRA Subtitle C or
TSCA-compliant landfill. Alternative 2 uses a different disposal technology, contained aquatic disposal,
which would make Section 404 of the Clean Water Act a more important ARAR for that alternative. Only
Alternative 5R-Treatment uses soil washing; however, ARARs for disposal or beneficial reuse of treated
material would be the same as for disposal of untreated sediments.
Table 12 summarizes the RALs for each alternative. Table 13 summarizes the areas and volumes and
associated with each remedial technology for each of the alternatives as well as costs and construction
durations. The cost of implementing cleanups at the EAAs is estimated at $95 million; this cost is not
included in the cost estimates for the alternatives.
Figure 14 shows a summary of technologies used, cleanup timeframes, and cost for each alternative.
Figure 15 shows the construction period and time for each alternative to achieve a range of risk reduction
benchmarks.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Remedial Alternatives and Technologies1
Remedial Action Levels1
Actively
Remediated
Area
(Acres)
PCBs
(mg/kg OC)
Arsenic
(mg/kg dw)
Dioxins/
Furans
(ng TEQ/kg dw)
cPAHs
((jg TEQ/kg dw)
Benthic
SMS
(41 Contaminants)11
Alternative 1 No Further Action after removal or capping of Early Action Areas
n/a
n/a
n/a
n/a
n/a
29 acres
Alternative 2 (2R) - dredge emphasis with upland disposal/MNR
Alternative 2 with CAD (2R-CAD) - dredge emphasis with contained aquatic
disposal/MNR
65 to 110 (LDW-wide);
10-yr post-construction
target: 65c
93
50
5,500
CSL to 3 x CSL
10-yr post-const,
target: CSL
32 acres
Alternative 3 removal (3R) - dredge emphasis with upland disposal/MNR
Alternative 3 combined technologies (3C) - ENR/in situ /cap/MNR where
appropriate, otherwise dredge with upland disposal
65 (LDW-wide)
93 (LDW-wide)
28 (intertidal)
35 (LDW-wide)
28 (intertidal)
3,800 (LDW-wide)
900 (intertidal)
CSL toxicity or
chemistry
58 acres
Alternative 4 removal (4R) - dredge emphasis with upland disposal/MNR
Alternative 4 combined technologies (4C) - ENR/in situ /cap/MNR where
appropriate, otherwise dredge with upland disposal
12 to 35 (LDW-wide)
10-yr post-const,
target: 12c
57 (LDW-wide)
28 (intertidal)
25 (site-wide)
28 (intertidal)
1,000 (LDW-wide)
900 (intertidal)
SQS to CSL
10-yr post-const,
target: SQS
107 acres
Alternative 5 removal (5R) - dredge emphasis with upland disposal
Alternative 5 removal with treatment (5R-T) - dredge with soil washing
treatment and disposal/re-use
Alternative 5 combined technologies (5C) - ENR/in situ /cap where
appropriate, otherwise dredge with upland disposal
12 (LDW-wide)
57 (LDW-wide)
28 (intertidal)
25 (LDW-wide)
28 (intertidal)
1,000 (LDW-wide)
900 (intertidal)
SQS toxicity or
chemistry
157 acres
Alternative 6 removal (6R) - dredge emphasis with upland disposal
Alternative 6 combined technologies (6C) - ENR/in situ /cap where
appropriate, otherwise dredge with upland disposal
5 (LDW-wide)
15 (LDW-wide)
28 (intertidal)
15 (LDW-wide)
28 (intertidal)
1,000 (LDW-wide)
900 (intertidal)
SQS toxicity or
chemistry
302 acres
Preferred Alternative (5C Plus) - ENR/in situ /cap where appropriate,
otherwise dredge with upland disposal.
12 (LDW-wide)
65 (intertidal)
195 (subtidal
subsurface)
57 (LDW-wide)
28 (intertidal)
25 (LDW-wide)
28 (intertidal)
1,000 (LDW-wide)
900 (intertidal)
2 X SQS chemistry
(not to exceed CSL)1
or SQS toxicity
10-year post-const,
target: SQS
156 acres
a. LDW-wide remedial action levels are applied in the upper 10 cm of sediment throughout the LDW and in the upper 60 cm in potential scour areas (i.e., Recovery Category 1 areas). Intertidal remedial action
levels are applied in the upper 45 cm of sediment in intertidal areas (above -4 ft MLLW). An intertidal PCB RAL of 65 mg/kg OC was added in Alternative 5C Plus in the top 45 cm in intertidal areas.
Alternative 5C Plus added a subtidal PCB RAL of 195 mg/kg OC for top 60 cm in Recovery Category 2 and 3 areas in areas of potential vessel scour. These potential scour areas comprise: north of the 1st
Avenue South bridge (located at approximately RM 2) in water depths from -4 to -24 ft MLLW, and south of the 1 st Avenue S bridge, in water depths from -4 to -18 ft MLLW.
b. PCB RALs are normalized to organic carbon (OC) for consistency with the SMS, and because the organic content of sediments affects the bioavailability and toxicity of PCBs.
c. The RALs for SMS contaminants (except arsenic) are a range for Alternatives 2 and 4. The upper RALs are used where conditions for recovery are predicted to be more favorable (Recovery Category 3);
the lower RALs are used where conditions for recovery are predicted to be limited or less certain (Recovery Categories 1 or 2), or where the BCM does not predict recovery to the 10-yr post-construction
target concentration.
d. See Table 14 for these values.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Table 13. Remedial Alternative Areas, Volumes, and Costs
Remedial Alternative Technology and Areas
MNR(MNR
Total
Partial
ENR1
MNRTo
Below SQS in
Active
Construction
Net Present
Site -wide Remedial
EAAs
Dredge
Dredge and
Cap
in situ
SQS»
Alt 5C Plus)
Remedy
Total Dredge
Time Frame
Value Costc
Alternative
(acres)3
(acres)
Cap (acres)
(acres)
(acres)
(acres)
(acres)
(acres)
Volume (cy)
(years)
(SMM)
1 No Further Action
29
0
0
0
0
0
412
0
n/a
n/a
$9
2 Removal
29
29
3
0
0
148
232
32
580,000
4
$210
2 Removal with CAD
29
29
3
0
0
148
232
32
580,000
4
$200
3 Removal
29
50
8
0
0
122
232
58
760,000
6
$270
3 Combined Technology
29
29
8
11
10
122
232
58
490,000
3
$200
4 Removal
29
93
14
0
0
73
232
107
1,200,000
11
$360
4 Combined Technology
29
50
18
23
16
73
232
107
690,000
6
$260
5 Removal
29
143
14
0
0
23
232
157
1,600,000
17
$470
5 Removal with Treatment
29
143
14
0
0
23
232
157
1,600,000
17
$510
5 Combined Technology
29
57
23
24
53
23
232
157
750,000
7
$290
Preferred Alternative
(5 Combined Technology Plus)
29
64
20
24
48
33
223
156
790,000
7
$305
6 Removal
29
274
28
0
0
0
110
302
3,900,000
42
$810
6 Combined Technology
29
108
42
51
101
0
110
302
1,600,000
16
$530
a. The 29 acres addressed by the EAAs are not included in area estimates for other alternatives.
b. Includes areas that the FS predicted will have naturally recovered enough that concentration levels are below the SQS by the time sampling is conducted for remedial design
(called "verification monitoring" in the FS).
c Net Present Value calculated using a 2.3% annual discount rate
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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62
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Proposed Plan — Lower Duwamish Waterway Superfund Site
> <
"rc <5
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Alternative 1
n/a
n/a
25 years
$9 Million
LEGEND
Acres pertechnology
Remedial Alternative
Comparative analysis
EAAs
Dredge and Partial Dredge and Cap
Cap
ENR
MNR to SQS
ICs and Site-wide Monitoring
MNR to Human Health PRGs
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Alternative 2 Removal with CAD
Alternative 2 Removal Emphasis
4 years
580,000 cy
24 years
$200 Million
4 years
580,000 cy
24 years
$220 Million
Alternative 3 Combined Technologies
3 years
490,000 cy
18 years
$200 Million
Alternative 3 Removal Emphasis
) years
760,000 cy
21 years
$270 Million
> <
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TO QJ
E "TO
.2 "5
< E
Alternative 4 Combined Technologies
Alternative 4 Removal Emphasis
6 years
690,000 cy
21 years
$260 Million
11 years
1,200,000 cy
21 years
$360 Million
> <
is ^
TO o
E "ra
.£ "5
< E
Alternative 5 Combined Technologies
Alternative 5 Removal Emphasisf5 Removal Emphasis
followed by Soil Washing
Alternative 5c Plus ¦ Preferred Remedy
7 years
750,000 cy
17 years
$290 Million
17 years
1,600,000 cy
22 years
$470 Million/$510 Million
7 years
790,000 cy
17 years
$305 Million
> <
is
TO 03
E "TO
£ ^
% 03
< E
Alternative 6 Combined Technologies
Alternative 6 Removal Emphasis
16 years
1,600,000 cy
16 years
$530 Million
42 years
3,900,000 cy
42 years
$810 Million
Figure 14. Summary of Alternatives
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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64
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Alt 1
1a,
>a,4 2
c
b
1c
2b
Alt 2R1 2R-CAD
19,23,20,4
lb
1
3
1
2b
1
tc
1
AltSC
ta,2a,2b,2c.4
1b,3
1c
1
I
Remedial
Alternative
Times to Achieve Individual Cleanup Objectives
Individually and Combined (years)
Alt
2a,2c
1a,2b4
lb,3
1
1c
1
RA01
RAO 2
RAO 3
RAO 4
All Four
1
25
25
20
5
25
2R/2R-CAD
24
18
14
4
24
Alt 4C
2a,2b,2c
la, 3,4
1b
I
1c
I
3D
18
3
8
3
18
3R
21
6
11
6
21
4C
21
3
6
6
21
Alt 4R
2a,2c
a
la,lb,3,4
1c
I
4R
21
6
11
11
21
5C
17
3
6
7
17
5CP1US
17
3
6
7
17
AltSC
2a.2b.2c
la, lb,4
1c
6C
16
3
6
16
16
1
5R
42
6
11
42
42
Alt SR /5R-T
2a,2c
a
3
1a, lb, 4
1c
I
AltSC
2a.2b.2c
3
la,1b,1c4
2a,2c
2b
3
!a,1b,1c,4
Alt6R
Alt 5c Plus - Preferred
2a,!b,2c 3 1a,1b,4
1c
1
Alternative
1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 29 21 22 23 24 2S 26 27 28 29 30 31 32 33 34 35 36 37 35 38 40 41 42 43 44
Time (years from start of construction)
2b
KEY: | _ Construction Period Pos-tonarucSsn naairai recovery period |Year the risk reduction metric is achieved
Chart Chart
RAO Symbol Metrics) raq Symbol Metric(s)
1 1a 10"4 magnitude risk for Adult Tribal, Child Tribal, and Adult API RME seafood consumption scenarios (only total PCB: 2 2a <1 x10~5 total direct contact risk and HQ<1 in all exposure areas
1 b 10"5 magnitude risk for Child Tribal RME seafood consumption scenario (only total PCBs) < 1 x 10"6 direct contact risk from total PCBs in all areas
1c Total PCBs and dioxin/furans reach long-term model-predicted ranges of site-wide SWACs < 1 x 10"5 and > 1 x 10"6 direct contact risk from arsenic in all areas
3 3 SQS (>98% of LDW area below SQS) 2b < 1 x 10"® direct contact risk from dioxins/furans in all areas
|T"™* —
4 4 HQ <1 (River Otter} < 1 x lO^direct contact risk from cPAHs in all areas except Beach 3
2c Arsenic reaches long-term model-predicted range of site-wide SWACs
Notes:
1. None of the alternatives are predicted to achieve a non-cancer HQ below 1 for three RME seafood consumption scenarios (see T able 9-7b of Final FS for details).
2. None of the alternatives are predicted to achieve sediment PRGs that are based on natural background: total PCBs and dioxins/furans - seafood consumption (RA01); arsenic - direct contact all scenarios (RAO 2).
Figure 15. Time to Achieve Risk Benchmarks for All Alternatives
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Alternative 1 - No Further Action - This alternative would not implement any further action following
removal or capping implemented through Early Actions, with the exception of continued LDW-wide
monitoring. It includes no ICs other than the existing seafood consumption advisories and those
implemented for the Early Actions. This alternative provides a baseline to compare the other remedial
alternatives against; its inclusion is required by CERCLA. LDW-wide monitoring costs, at present value
(PV), for Alternative 1 are estimated to be $9 million.
Alternatives 2R and 2R-CAD - These alternatives would
actively remediate 32 acres with contaminant
concentrations above the Alternative 2 RALs (Table 12).
The area and volume of contaminated sediments
remediated by each technology and estimated costs are
provided in Table 13. Alternatives 2 and 2R include:
• For areas with COC concentrations exceeding the
RALs, Alternative 2R includes dredging with upland
landfill disposal, while Alternative 2R-CAD adds
contained aquatic disposal (CAD) to address disposal
of some of the dredged material.
• In areas with COC concentrations below the RALs,
MNR would be used to reduce COC concentrations to
the SQS (RAO 3) within 20 years following
construction as well as to achieve cleanup objectives6
for RAOs 2 and 4. As noted above, the FS makes no
distinction between MNR To SQS and MNR Below
SQS, so these terms are not used for any alternative except the Preferred Alternative (5C Plus). As
discussed in Section 8.2.1, the FS used the term "MNR" to include enhanced monitoring and
additional actions only for any area where COC concentrations are not reduced to the SQS levels. For
simplicity, this Proposed Plan uses the term MNR to refer to all areas where COC concentration
reduction is predicted, to levels both above and below the SQS.
• Seafood consumption advisories, outreach, and education programs would be used to further reduce
exposure to contamination in fish and shellfish, and proprietary controls such as environmental
covenants would be used to reduce the likelihood of exposure where contamination remains above
cleanup levels.
These alternatives are designed to achieve the following at a minimum, relative to the RAOs for the in-
waterway portion of the Site:
• For RAO 1 (human health seafood consumption): Incremental risk reduction through active
remediation and further risk reduction through MNR.
6. The term "cleanup objectives" is used in the FS to mean the PRG or as close as practicable to the PRG where the
PRG is not predicted to be achievable. The FS uses long-term model-predicted concentrations as estimates of "as
close as practicable" to PRGs.
Remedial Action Objectives
RAO 1: Reduce to protective levels human health
risks associated with the consumption of
contaminated resident LDWfish and shellfish by
adults and children with the highest potential
exposure.
RAO 2: Reduce to protective levels human health
risks from direct contact (skin contact and
incidental ingestion) of contaminated sediments
during netfishing, clamming, and beach play.
RAO 3: Reduce to protective levels risks to
benthic invertebrates from exposure to
contaminated sediments.
RAO 4: Reduce to protective levels risks to crabs,
fish, birds, and mammals from exposure to
contaminated sediment, surface water, and prey.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
• For RAO 2 (human health direct contact): Meet cleanup objectives within 10 years following
construction.
• For RAO 3 (protection of benthic community): Reduce contaminants in sediment to meet the CSL
within 10 years following construction, and the SQS within 20 years following construction. (See
Section 4.2 for additional information on CSL and SQS).
• For RAO 4 (protection of river otter): Meet PRG within 10 years following construction.
Alternatives 3R and 3C - These Alternatives actively remediate 58 acres with contaminant
concentrations above the Alternative 3 RALs (Table 12). The area and volume of contaminated sediments
remediated by each technology and estimated costs are provided in Table 13. A greater amount of surface
and subsurface contamination is removed by these alternatives than Alternative 2, and they rely more on
active remediation to reduce risks to human health from consuming contaminated seafood than the
previous alternatives. Alternatives 3R and 3C include:
• For areas exceeding the RALs, Alternative 3R has a removal emphasis (i.e., dredging) with upland
disposal/MNR, and Alternative 3C uses a combined technology approach (i.e., capping and
ENR/MNR/in situ treatment) in addition to dredging with upland disposal.
• MNR is used in areas with concentrations below RALs to achieve the SQS within 20 years following
construction, with additional COC concentration reduction overtime to the cleanup objectives.
• ICs would be used as described in Alternative 2.
These alternatives are designed to achieve, at a minimum, the outcomes of Alternative 2, plus:
• For RAO 1: Achieve greater reduction of risk because there is a larger area of active remediation.
• For RAOs 2 and 4: Achieve cleanup objectives immediately following construction, rather than 10
years following construction.
• For RAO 3: Achieve the CSL immediately following construction, rather than 10 years following
construction. The SQS would still not be projected to be reached for 20 years.
Alternatives 4R and 4C - These alternatives actively remediate 107 acres with contaminant
concentrations above the Alternative 4 RALs (Table 12). The area and volume of contaminated sediments
remediated by each technology and estimated costs are provided in Table 13. MNR is used in areas with
concentrations below the RALs to achieve the SQS within 10 years following construction, with
additional COC concentration reduction overtime to the cleanup objectives. ICs would be used as
described in Alternative 2. Alternatives 4C and 4R rely more on active remediation than previous
alternatives to reduce COC concentrations. These alternatives are designed to achieve, at a minimum, the
outcomes of Alternative 3, plus:
• For RAO 1: Achieve greater risk reduction because there is a larger area of active remediation.
• For RAOs 2 and 4: Same as Alternative 3.
• For RAO 3: Achieve the SQS for within 10 years following construction as opposed to 20 years
following construction.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Alternatives 5R, 5R-Treatment, and 5C -These alternatives actively remediate 157 acres with
contaminant concentrations above the Alternative 5 RALs (Table 12). The area and volume of
contaminated sediments remediated by each technology and estimated costs are provided in Table 13.
These three alternatives do not use MNRto reach the SQS7, however, MNR is relied upon to further
reduce risks to the cleanup objectives. Alternative 5R-Treatment utilizes removal with ex situ treatment
(soil washing) and disposal/re-use. These three alternatives rely more on active remediation than previous
alternatives to reduce COC concentrations. These alternatives are designed to achieve, at a minimum, the
outcomes of Alternative 4, plus:
• For RAO 1: Achieve greater risk reduction because there is a larger area of active remediation.
• For RAOs 2 and 4: Same as Alternative 3.
• For RAO 3: Achieve the SQS immediately following construction as opposed to 10 years following
construction.
Alternatives 6R and 6C - These alternatives actively remediate 302 acres with contaminant
concentrations above the Alternative 6 RALs (Table 12). The area and volume of contaminated sediments
remediated by each technology and estimated costs are provided in Table 13. Alternative 6R has a
dredging emphasis with upland disposal, while Alternative 6C emphasizes combined technologies
including ENR/capping where appropriate, in addition to dredging with upland disposal. These
alternatives are designed to achieve, at a minimum:
• For RAO 1: Achieve the lowest model-projected COC concentrations immediately after construction,
rather than relying on MNR.
• For RAOs 2 and 4: Same as Alternative 3.
• For RAO 3: Achieve the SQS immediately following construction as opposed to 10 years following
construction.
Alternatives 6C and 6R rely the most on active remediation to reduce COC concentrations relative to all
other alternatives.
Preferred Alternative (5C Plus) - Alternative 5C Plus was developed by modifying FS Alternative 5C
to include additional remedial elements as described in the FS Supplement (see Key Documents). The FS
Supplement evaluated these additions to address several concerns, including the need for:
• Additional RALs for subsurface sediments in areas outside of Recovery Category 1 areas to address
the potential that subsurface contamination could be disturbed and exposed at the surface through
activities such as emergency or high-power vessel operations, vessel groundings, maintenance
activities, or earthquakes;
• Additional dredging in shoaled areas of the navigation channel where COC concentrations exceed
RALs to address the potential that subsurface contamination could be disturbed through maintenance
dredging;
• Increased cap thickness in intertidal clamming areas to provide adequate habitat for clams; and
7. Although Table 12 shows 23 acres of MNR, the FS predicts that COC concentrations in these areas will be
reduced to the SQS prior to the start of construction.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
• Increased sediment monitoring to evaluate natural recovery progress in areas where COC
concentrations are below the SQS but above PRGs (designated as MNR Below SQS in this Proposed
Plan).
In addition, the FS Supplement evaluated greater use of MNR to reduce concentrations of non-human
health COCs in surface sediments, while continuing to use active remediation when RALs for human
health COCs are exceeded.
Six scenarios were developed in the FS Supplement. EPA, in consultation with Ecology, selected FS
Supplement Scenario 5a (referred to as Alternative 5C Plus or the Preferred Alternative in this Proposed
Plan). Estimates of cleanup areas and volumes for Alternative 5C Plus were then further refined in a
February 2013 memorandum8: Alternative 5C Plus actively remediates 156 acres with contaminant
concentrations above the Alternative 5C Plus RALs (Table 12 and Table 14). These RALs are the same as
for Alternative 5, except:
• To address the concern that high concentrations of PCBs, the most prevalent COC in the LDW, could
become exposed through human activities such as digging in the beach in intertidal areas or
emergency ship maneuvering in intertidal or subtidal areas, new subsurface PCB RALs were added in
Recovery Category 2 and 3 areas. For subsurface sediments in intertidal areas, the PCB RAL is 65
mg/kg OC, and for subtidal areas it is 195 mg/kg OC. No other alternatives have subsurface RALs
for PCBs in Recovery Category 2 and 3 areas.
• The RALs for non-human health COCs in surface sediments were increased to 2 times the SQS, not
to exceed the CSL, in Recovery Category 2 and 3 areas. The SQS must be met within 10 years of
completing remedial action.
The area and volume of contaminated sediments remediated by each remedial technology and the
estimated costs are provided in Table 13. Alternative 5C Plus includes 33 acres of MNR To SQS, and 223
acres of MNR Below SQS (with more monitoring than in the FS Alternatives) for RAO 1. Alternative 5C
Plus would rely more on active remediation than 5C (but less than 6C) to reduce COC concentrations in
surface sediments. Alternative 5C Plus is designed to achieve, at a minimum, the following outcomes:
• For RAOs 1, 2 and 4: Achieve greater risk reduction than 5C because there would be a larger volume
of sediments actively remediated, and an increased emphasis on reducing high concentrations of
PCBs in subsurface sediments.
• For RAO 3: Achieve the CSL immediately following construction, and the SQS within 10 years
following construction.
8. Development of Final Technology Assignments and Modifications to Alternative 5C Plus Scenario 5 a in Support
of EPA's Preferred Alternative; see Key Documents.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Table 14. Alternative 5C Plus Ecological Risk Reduction (Benthic Protection) RALs
SMS Contaminant of Concern
RAL for Recovery Category 1
Areas3 (SQS)
RAL for Recovery Category 2 & 3
Areas (2 x SQS or CSL, whichever
is lower)
Metals (mg/kg dw)
Cadmium
5.1
6.7b
Chromium
260
270b
Copper
390
390b
Lead
450
530b
Mercury
0.41
0.59b
Silver
6.1
6.1b
Zinc
410
O
CM
CO
PAHs (mg/kg OC)
2-Methylnaphthalene
38
64b
Acenaphthene
16
32°
Anthracene
220
440°
Benzo(a)anthracene
110
220°
Benzo(a)pyrene
99
198°
Benzo(g,h,i)perylene
31
62°
Total benzofluoranthenes
230
450b
Chrysene
110
220°
Dibenzo(a,h)anthracene
12
24°
Dibenzofuran
15
30°
Fluoranthene
160
O
CM
CO
Fluorene
23
46°
lndeno(1,2,3-cd)pyrene
34
68°
Naphthalene
99
198b
Phenanthrene
100
O
O
CM
Fyrene
1,000
1,400b
Total HPAHs
960
1,920°
Total LPAHs
370
740°
Phthalates (mg/kg OC)
Bis(2-ethylhexyl)phthalate
47
78b
Butyl benzyl phthalate
4.9
9.8°
Dimethyl phthalate
53
53b
Chlorobenzenes (mg/kg OC)
1,2,4-Trichlorobenzene
0.81
1.62°
1,2-Dichlorobenzene
2.3
2.3b
1,4-Dichlorobenzene
3.1
6.2°
Hexachlorobenzene
0.38
0.76°
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Proposed Plan — Lower Duwamish Waterway Superfund Site
SMS Contaminant of Concern
RAL for Recovery Category 1
Areas3 (SQS)
RAL for Recovery Category 2 & 3
Areas (2 x SQS or CSL, whichever
is lower)
Other SVOCs and COCs. (jug/kg dw except as shown)
2,4-Dimethylphenol
29
29"
4-Methylphenol
670
670b
Benzoic acid
650
650b
Benzyl alcohol
57
73b
n-Nitrosodiphenylamine, mg/kg OC
11
11b
Pentachlorophenol
360
690b
Phenol
420
00
o
PCBs and arsenic are not shown because they are also human health COCs. The site-wide surface sediment RALs
for these contaminants are the SQS.
a. As noted in Table 12, for Recovery Category 1 areas, the SQS is the RAL to 10 cm and 45 cm for intertidal zones
and to 10 cm and 60 cm for subtidal areas.
b. Based upon CSL, which is less than 2 x SQS
c. Based upon 2 x SQS
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Proposed Plan — Lower Duwamish Waterway Superfund Site
9 Evaluation of Alternatives
EPA used the nine criteria required by CERCLA and the NCP to evaluate and select a preferred
alternative for the in-waterway portion of the LDW Superfund Site. This section describes the relative
performance of each alternative against the nine criteria, noting how the Preferred Alternative, 5C Plus,
compares to the other alternatives. The findings and recommendations in EPA's EJ Analysis (Appendix
B) were also considered as part of the CERCLA nine criteria analysis.
The nine criteria are in three categories: threshold criteria, primary balancing criteria, and modifying
criteria.
Nine Criteria for CERCLA Remedy Selection
Threshold criteria. Each alternative must meet threshold criteria to be eligible for selection.
Overall Protection of Human Health and the Environment — addresses whether each alternative provides adequate
protection of human health and the environment and describes how risks posed through each exposure pathway are eliminated,
reduced, or controlled through treatment, engineering controls, and/or institutional controls.
Compliance with Applicable or Relevant and Appropriate Requirements (ARARs) — Section 121 (d) of CERCLA and NCP
§300.430(f)(1)(ii)(B) requires that remedial actions at CERCLA sites at least attain legally applicable or relevant and appropriate
Federal and State requirements, standards, criteria, and limitations which are collectively referred to as ARARs, unless such
ARARs are waived under CERCLA Section 121(d)(4).
Primary balancing criteria. Balancing criteria are used to evaluate the major technical, cost, and other trade-offs among the various
remedial alternatives.
Long-Term Effectiveness and Permanence — refers to expected residual risk and the ability of a remedy to maintain reliable
protection of human health and the environment over time, once cleanup levels have been met. This criterion includes the
consideration of residual risk that will remain onsite following remediation and the adequacy and reliability of controls.
Reduction of Toxicity, Mobility, or Volume Through Treatment — refers to the anticipated performance of the treatment
technologies that may be included as part of a remedy.
Short-Term Effectiveness — addresses the period of time needed to implement the remedy and any adverse impacts to
workers, the community, and the environment during construction and operation of the remedy until cleanup levels are achieved
(and how they may be mitigated).
Implementability— addresses the technical and administrative feasibility of a remedy from design through construction and
operation. Factors such as availability of services and materials, administrative feasibility, and coordination with other
governmental entities are also considered.
Cost — addresses the cost of construction and any long term costs to operate and maintain the alternative, in terms of estimated
capital, annual operation and maintenance, and total net present worth costs.
Modifying criteria. Modifying Criteria are considered to the extent that information is available during the FS, but will be fully
considered only after public comments are received on the Proposed Plan.
State /Tribal acceptance — Assessment of state concerns including (1) The State's position and key concerns related to the
Preferred Alternative and other alternatives; and (2) State comments on ARARs or the proposed use of ARAR waivers. Concerns
of affected Tribes are also considered.
Community acceptance — This assessment includes determining which components of the alternatives interested persons in
the community support, have reservations about, or oppose.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
9.1 Threshold Criteria
An alternative must meet the two threshold criteria to be eligible for selection as a remedial action.
9.1.1 Overall Protection of Human Health and the Environment
All of the alternatives except Alternative 1 provide a substantial reduction in risk when compared to
baseline conditions. They meet the threshold criterion of overall protection of human health and the
environment over varying timeframes, providing an adequate level of protection with varying degrees of
reliance on natural recovery and institutional controls. The objective of all alternatives is to reach PRGs in
the long term; however, alternatives that rely more on natural recovery have greater uncertainty in their
projected outcomes, and are predicted to take longer to reach steady state in the waterway; see Figure 15.
Risk at PRGs. Estimated cancer and non-cancer risks for the adult Tribal RME seafood consumption rate
after cleanup to the fish and shellfish tissue PRGs for all COCs (which, for some COCs, are based on
natural background levels that are higher than calculated protective risk-based levels [RBTCs], see Table
10) are estimated to be 3 in 10,000, above the excess cancer risk thresholds in CERCLA and MTCA
(Figure 16), mainly due to the contribution of arsenic and dioxins/furans. At PRG levels, none of the 4
human health COCs meet the MTCA individual carcinogen risk threshold of 1 in 1,000,000, nor do they
together meet the MTCA excess cancer risk threshold of 1 in 100,000 for multiple contaminants. Thus,
even if all PRGs are achieved, seafood consumption advisories will be needed to provide adequate
protectiveness. At PRG levels, the HQ for non-cancer risks is less than the CERCLA and MTCA
threshold of 1 (based on PCBs, the COC with the highest HQ).
Risk at model-predicted steady state concentrations. As discussed in Section 7, RI/FS models (the
STM, the BCM, and the food-web model) predicted that for all alternatives, LDW sediment and tissue
COC concentrations would reach a long-term steady state at concentrations higher than the risk- and non-
urban background-based sediment and tissue PRGs. The magnitudes and types of risks to humans,
wildlife, and the benthic community from PCBs that would remain in surface sediments after
implementation of the cleanup alternatives were estimated through the use of natural recovery modeling
(which predicts future sediment contaminant concentrations) and a food-web model (which predicts the
movement of contaminants from sediments and water to organisms). Only PCBs could be addressed in
the RI/FS food-web model, because RI data did not provide sufficient information to develop predictable
relationships between sediment concentrations and tissue concentrations for arsenic and cPAHs, and
because of insufficient tissue data for dioxins/furans9. The FS estimated an adult Tribal RME excess
cancer risk of 2 in 10,000 and non-cancer risk of HQ of 4 for PCBs only at the model-predicted steady
state (Figure 17). An important distinction between this and the risks estimated at the PRG levels
discussed above is that these FS seafood consumption residual risk estimates have been calculated for
PCBs only, whereas the risks estimates at the PRGs discussed above have been calculated for all COCs.
Risks for PCBs only at the tissue PRG are estimated to be 5 in 1,000,000 and HQ of less than 1. These
estimates of post-cleanup risks represent a reduction in PCB risks of approximately 90% at the model-
predicted steady state and 99% at the PRG for the adult Tribal RME seafood consumption rate when
compared to baseline risks presented in Section 4.1.
9. Additional studies will be performed during the design phase to collect more data on baseline fish and shellfish
COC concentrations and consider whether and by what means arsenic and cPAH tissue concentrations in clams (the
only species showing high risks for these COCs) can be reduced.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Risks at a range of seafood consumption rates. Calculating health risks from eating fish or shellfish is
critically dependent on how much seafood a person may eat. None of the alternatives would allow for
consumption of resident fish and shellfish at the high consumption rates reported for Tribal or Asian
Pacific Islander populations, even if they were to meet the PRGs. However, at the proposed PRGs or
even some model-projected steady state COC concentrations, people who consume moderate or small
amounts of fish and shellfish from the LDW would be protected. Figure 16 shows estimated cancer and
noncancer risks at the PRGs at a range of consumption rates for different seafood types. At a consumption
rate of one meal every other month, seafood consumption risks for all seafood types except crab whole
body are at or below the MTCA excess cancer risk threshold for multiple contaminants of 1 in 100,000.
Figure 17 compares PCB risks for the current condition (baseline), at the model-predicted steady state
concentrations, and at tissue PRG concentrations.
All alternatives achieve protectiveness for seafood consumption at the RME seafood consumption rates
through varying combinations of: 1) reduction of contaminant concentrations through active remediation,
2) MNR, and 3) institutional controls designed to reduce exposure, especially from consumption of
resident LDW seafood. EPA's intent is for the selected remedy to achieve risk reduction and
protectiveness while minimizing reliance on seafood consumption-related Institutional Controls to the
extent practicable. Alternative 1 would not protect human health and the environment. It does not include
any active cleanup or institutional controls beyond the current Washington Department of Health
(WDOH) health advisory, and those controls implemented at EAAs. It is therefore not discussed further.
The time to achieve a range of risk benchmarks for each alternative is summarized in Figure 15. The
RI/FS models predicted that Alternatives 2-6 would reach the lowest model-predicted concentrations and
associated risks described above in 16 to 42 years. The amount of time to reach the estimated risk
reduction at the PRGs could not be predicted by the model because it predicted that LDW COC
concentrations would reach steady state at concentrations higher than the PRGs. However, model
predictions are uncertain and necessarily limited to technologies available at the time of the modeling.
Long-term model-predicted COC concentrations in the LDW are highly dependent on COC
concentrations in incoming Green/Duwamish River water and suspended sediments (in addition to the
extent of sediment remediation and the extent to which ongoing contaminant sources within the LDW
drainage basin are addressed). As noted previously, all projections used in the Proposed Plan also use
current conditions in the Green/Duwamish and do not consider additional sampling currently being
conducted by Ecology and King County to better understand Green/Duwamish River inputs to the LDW
and potential reductions due to source control in the Green/Duwamish watershed. These projections may
be refined during the remedial design phase.
For direct contact with sediments in netfishing, clamming, and beach play areas (RAO 2), all alternatives
are predicted to result in risks within the CERCLA risk range and meet the minimum MTCA
requirements for risk reduction: 1) a total excess cancer risk of less than 1 in 100,000 cumulatively for all
COCs; 2) excess cancer risks for individual COCs less than or equal to 1 in 1,000,000 (except for
arsenic), and 3) non-cancer HI less than or equal to 1. The natural recovery model predicts arsenic will
reach an excess cancer risk range below 1 in 100,000 but above 1 in 1,000,000. Alternative 2 requires a
period of natural recovery to meet these objectives which means higher uncertainty in the modeling
projections for these outcomes, whereas Alternatives 3-6 meet them after construction.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
c
(0
tJuQ
o
C
1 in 100 "
1 in
1,000
^ J2
X
o
o
u
c
A3
(A (J
s °-
® X
ffl <
E
u
^ 1
o
E
3
l/l
lin
10,000
1 in
100,000
1 in
000,000
10
1 in
,000,000
¦ English sole (fillet) §
Crab (edible meat) §
I Clam
I Perch (whole body) §
! Crab (whole body) §
Market Basket
The shaded area indicates EPA's acceptable cancer risk range under CERCLA.
The dotted line indicates the MTCA threshold for the sum of multiple carcinogens
!*«¦¦¦¦¦¦¦¦¦
1 meal every
other month
1 mea
per month
1 meal
per week
3 meals
per week*
CD
u
a,
i-
£
c
-------
Proposed Plan — Lower Duwamish Waterway Superfund Site
u
a.
c
rc
u
1 in
100
lin
1,000
1 in
10,000
lin
100,000
1,000,000
1 in
10,000,000
i Risks at LDW baseline concentrations
Risk at model-predicted steady state concentrations
Risk at PRG
1 meal every
other month
1 meal
per month
1 meal
per week
3 meals
per week*
c
V
*3
O
2
a
"e a
s*
OJ
c
o
Z
14
12
10 -
8
6
i HQ at LDW baseline
concentrations
HQ at model-predicted
steady state concentrations
HQ at PRG
38
1 meal every
other month
1 meal
per month
1 meal
per week
3 meals
per week*
risks at model-predicted steady-state concentrations are 90% lower than risks at LDW baseline
risks at PRGs are 9994 lower than risks at LOW baseline
0%
20% 40% 60%
Reduction in Risk/HQ Relative to Baseline
80%
100%
Exposure assumptions: Excess cancer risks and non-cancer hazard quotients (HQs) were calculated assuming market basket consumption using the exposure
assumptions for the adult tribal RME seafood consumption scenario. Three meals per week is approximately equal to the consumption rate used for the adult Tribal
RME Scenario in the HHRA. A meal is equal to 8 ounces.
Lifetime excess cancer risks and non-cancer HQs shown in this figure are only for total PCBs; the calculation of total risks for the site would include all contaminants.
Excess cancer risks and non-cancer HQs were calculated using a) LDW baseline tissue concentrations from the LDW HHRA; b) model-predicted steady-state tissue
concentrations, based on predictions of tissue concentrations using the calibrated LDW food web model at a sediment concentration of 40 pg/kg dw and a water
concentration of 0.6 ng/L; and c) PRG concentrations, based upon either the higher of either non-urban Puget Sound tissue concentrations or the species-spectfic
tissue RBTCs.
Risk thresholds: In the top portion of the figure showing the excess cancer risks, the shaded area indicates EPA's acceptable excess cancer risk range under
CERCLA. The dotted line indicates the MTCA threshold for individual carcinogens. In the tower portion of the figure showing non-cancer HQs, the dotted line
indicates the CERCLA and MTCA non-cancer threshold
Figure 17. Comparison of Total PCB Excess Cancer Risks and Non-cancer HQs for Seafood
Consumption Calculated using LDW Baseline, Model-predicted, and PRG Concentrations
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Proposed Plan — Lower Duwamish Waterway Superfund Site
All alternatives are predicted to achieve the SQS, the PRGs for protection of benthic invertebrates (RAO
3), in 6 to 20 years. Alternatives 2 to 4 and 5C Plus rely on MNR To SQS to reduce COC concentrations
to the SQS, with more reliance (and greater uncertainty) in lower-numbered alternatives. Alternative 5C
Plus differs from Alternatives 2 - 4 in that it relies on MNR To SQS to reduce COC concentrations only
for non-human health COCs.
All alternatives are predicted to achieve the RAO 4 PRG for protection of wildlife (river otters) shortly
following construction. Alternatives 2 and 3 are predicted to require a short period of natural recovery to
achieve the PRG.
It is EPA's expectation that after implementation of the actions anticipated in Alternatives 2-6, along
with source control activities for which Ecology has the lead, levels in the sediment, surface water, and
fish and shellfish tissue will be protective of all anticipated uses, with the addition of fish and shellfish
consumption advisories.
9.1.2 Compliance with ARARs
Key ARARs for the cleanup alternatives are shown in Table 15. The most important ARARs are MTCA
and Federal and State water quality standards and criteria (both of which include the SMS). MTCA
requires final cleanup levels to be set at natural background concentrations when MTCA RBTCs10 are
below natural background. The objective of each of the alternatives is to meet ARARs throughout the in-
waterway portion of the LDW. However, as discussed above, the RI/FS models indicate that the long-
term COC sediment concentrations achievable in the in-waterway portion of the LDW will be limited by
the extent to which all ongoing sources, including COCs entering the waterway from the upstream
Green/Duwamish River system and remaining lateral sources, can be controlled in this urban
environment. Specifically, the RI/FS models indicate that while remediation is predicted to result in
significant improvements in sediment and tissue COC concentrations, it is not predicted to achieve
sediment PRGs based on MTCA ARARs for PCBs, dioxins/furans (for RAO 1), and arsenic (for RAO 2);
and fish and shellfish tissue PRGs for PCBs, arsenic, cPAHs and dioxins/furans. In addition, current
concentrations of PCBs in the upstream Green/Duwamish River are higher than Federal Ambient Water
Quality Criteria (AWQC) and the RI/FS model projections assumed no future decrease in the current
upstream concentration.
Based on the uncertainties in model projections, and particularly in estimates of COC concentrations in
incoming sediments from the Green/Duwamish River, each of the alternatives can potentially meet
ARARs in spite of RI/FS model projections suggesting otherwise. As discussed under Long-Term
Effectiveness and Permanence, uncertainty in achieving some ARARs increases with increasing reliance
on natural recovery because natural recovery outcomes are generally more uncertain than active
remediation. The objective of the Preferred Alternative and Ecology's source control program is to reduce
COC concentrations to natural background or risk-based PRGs. EPA expects to monitor progress of these
actions, including measuring long-term COC concentrations in sediment, fish and shellfish tissue, and
10. MTCA requires a total excess cancer risk of less than or equal to 1 in 100,000 and excess cancer risks for
individual COCs less than or equal to 1 in 1,000,000 and a non-cancer HQ or HI of less than 1.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
surface water. EPA will evaluate the results the actions have achieved over time in terms of ARAR
compliance as well as protectiveness.
PRGs for the protection of benthic invertebrates (RAO 3) are based on the SMS. Over time, all of the
alternatives are predicted to reduce contaminant concentrations to the SQS. However, Alternative 2 may
not do so within 10 years following active remediation (based on model prediction uncertainty), as
required by the SMS to the extent practicable.
To protect threatened species under the ESA, including Puget Sound Chinook salmon, environmental
windows (also known as "fish windows") have been established for the LDW. These are designated
periods (generally from October through February), when effects of in-water construction on spawning,
rearing, and habitat are minimized, largely because juvenile salmon are not migrating through the
waterway during that period. EPA will consult with the National Marine Fisheries Service to ensure
protection of threatened salmon species.
If long-term monitoring data and trends indicate that some ARARs-based cleanup levels selected in the
ROD after public comment on this Proposed Plan are not met, a waiver of these ARARs could be
considered by EPA in a future decision document (ROD Amendment or Explanation of Significant
Differences [ESD]). For example, if monitoring shows such levels have reached the SQS but have not
reached the surface water PRGs or human health and natural background-based sediment PRGs, and EPA
were to conclude that no further action would practicably improve these levels, the ARARs that are not
met would be eligible for a technical impracticability (TI) waiver. Because EPA cannot know whether
and to what extent ARARs for these various levels for different COCs will be achieved, consideration of
the potential for such a waiver prior to the collection of monitoring data sufficient to inform any TI
waiver decision(s) is neither warranted nor justifiable.
The ARARs discussed in this Proposed Plan apply only to EPA's in-waterway cleanup and should not be
construed to govern actions under other laws.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Table 15, Key ARARs for the LOW
Topic
Standard or
Requirement
Regulatory Citation
Comment
Federal
State
Hazardous
Substances
Requirements for
all affected media
Model Toxics Control Act
(Chapter 70.105D RCW, WAC 173-
340)
All substantive MTCA requirements are ARARs to
the extent they are more stringent than CERCLA
requirements. Key more stringent requirements
include acceptable excess cancer risk standards,
the default to natural background for final remedies
where risk-based cleanup levels are below
background, an institutional control (IC) mandate
and limits on IC usage.
Sediment Quality
Sediment quality
standards;
cleanup
screening levels
Sediment Management Standards
(WAC 173-204)
The SMS are MTCA rules and Water Quality
Standards under CWA and are an ARAR under
CERCLA. Numerical standards for the protection of
benthic marine invertebrates.
Surface Water
Quality
Surface Water
Quality
Standards
Ambient Water Quality Criteria established
under Section 304(a) of the Clean Water
Act (33 U.S.C. 1251 etseq)
http://www.epa.gov/ost/criteria/wqctable/
and National Toxics Rule (40 CFR 131.36)
Surface Water Quality Standards
(RCW 90-48;
WAC 173-201 A)
State surface water quality standards apply where
the State has adopted, and EPA has approved,
Water Quality Standards that are more stringent
than Federal recommended Water Quality Criteria
established under Section 304(a) of the Clean
Water Act. The National Toxics Rule applies for
human health criteria in the State of Washington.
Both chronic and acute standards, and marine and
freshwater are used as appropriate.
Land Disposal of
Waste
Disposal of ma
terials containing
PCBs
Toxic Substances Control Act (15 U.S.C.
2605; 40 CFR Part 761)
Hazardous waste
Resource Conservation and Recovery Act
Land Disposal Restrictions (42 U.S.C.
7401-7642; 40 CFR 268)
Dangerous Waste Regulations Land
Disposal Restrictions (RCW 70.105;
WAC 173-303,-140,-141)
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Topic
Standard or
Requirement
Regulatory Citation
Comment
Federal
State
Dredge/Fill and
Other In-water
Construction Work
Discharge of
dredged/fill
material into
navigable waters
or wetlands
Clean Water Act (33 U.S.C. 401 et seq; 33
U.S.C. 141; 33 U.S.C. 1251-1316; 40 CFR
230, 231, 404; 33 CFR 320-330) Rivers
and Harbors Act (33 U.S.C. 401 et seq.
Hydraulic Code Rules
(RCW 75.20;
WAC 220-110)
For in-water dredging, filling or other construction.
Open-water
disposal of
dredged
sediments
Marine Protection, Research and
Sanctuaries Act (33 U.S.C. 1401-1445)
40 CFR 227
Open Water Disposal Sites (RCW
79.90; WAC 332-30-166)
Solid Waste
Disposal
Requirements for
solid waste
handling
management and
disposal
Solid Waste Disposal Act (42 U.S.C.
215103259-6901-6991; 40 CFR 257, -
258)
Solid Waste Handling Standards
(RCW 70.95;
WAC 173-350)
Discharge to
Surface Water
Point source
standards for
new discharges
to surface water
National Pollutant Discharge Elimination
System (40 CFR 122, 125)
Discharge Permit Program (RCW
90.48;
WAC 173-216, -222)
Habitat for Fish,
Plants, or Birds
Evaluate and
mitigate habitat
impacts
Clean Water Act (Section 404 (b)(1)); U.S.
Fish and Wildlife Mitigation Policy (44 FR
7644);
U.S. Fish and Wildlife Coordination Act
(16 U.S.C. 661 etseq); Migratory Bird
Treaty Act (16 U.S.C. 703-712)
Critical Habitat for
Endangered
Species
Conserve
endangered or
threatened
species, consult
with species
listing agencies
Endangered Species Act of 1973 (16
U.S.C. 1531 etseq; 50 CFR200, -402);
Magnuson-Stevens Fishery Conservation
and Management Act (16 U.S.C. 1801-
1884)
Endangered, threatened, and
sensitive wildlife species
classification (WAC 232-12-297)
Consult and obtain Biological Opinions.
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9.2 Balancing Criteria
The balancing criteria evaluate the major trade-offs among alternatives.
9.2.1 Long-Term Effectiveness and Permanence
Although all alternatives are predicted by RI/FS models to result in the same long-term risks after
cleanup, as discussed in Section 9.1.1, alternatives that rely less on natural recovery have less uncertainty
in long-term model projections, though this uncertainty can be reduced to some extent through monitoring
and adaptive management, as is required for MNRTo SQS. The higher-numbered alternatives have
increasingly larger cleanup footprints, and rely progressively less on natural recovery to achieve cleanup
objectives.
Alternatives that remove more surface and subsurface contamination through dredging provide the most
permanence, followed by those that effectively isolate it through engineered caps. Dredged contaminated
sediment is permanently removed from the LDW, and capped sediment is securely segregated from
contact with receptors. Caps typically maintain their effectiveness as long as they are monitored and
maintained. Contamination remaining in subsurface sediments and not isolated by a cap would contribute
to future risks if they are brought to the surface of the waterway through natural or man-made events such
as earthquakes, vessel scour, or construction activities. ENR and MNR are not designed to isolate
contamination, so alternatives that use these in areas with lower contaminant concentrations provide
better long-term effectiveness than those that use them in areas with higher concentrations. The potential
for increased surface COC concentrations through disturbance of subsurface sediments is not accounted
for in the BCM; thus the BCM may underestimate the long-term COC concentrations.
All alternatives require that RALs be met in the top 60 cm in Recovery Category 1 areas to address the
potential for exposure of subsurface contamination in the areas where disturbance is most likely. All
alternatives also require that direct contact (RAO 2) RALs for arsenic, cPAHs, and dioxins/furans be met
in the top 45 cm to protect people clamming or digging on the beach. However, it is not possible to
anticipate every location where disturbance might occur. Alternative 5C Plus adds PCB RALs of 65
mg/kg OC in the top 45 cm in intertidal sediments to reduce the potential for exposure of subsurface
contamination through digging on the beach, and 195 mg/kg OC in the top 60 cm of subtidal sediments to
reduce the influence of activities such as vessel scour11. Only alternatives 5R, 6C, and 6R would remove
more subsurface contamination in all potentially erosive areas than 5C Plus.
Monitoring of sediment, fish and shellfish tissue, and surface water will be required under all remedial
alternatives. Areas that are dredged require the least long-term sediment monitoring. Capping and ENR
require more sediment monitoring to ensure surface concentrations remain low. MNR requires the most
11. The FS Supplement evaluated several options for subsurface RALs. EPA selected the 5C Plus RALs listed here
because other options removed less subsurface contamination with an associated increased risk of exposure, or
removed more subsurface contamination at a higher cost that was disproportional to the increase in long-term
effectiveness and permanence. The 60 cm PCB RAL of 195 mg/kg OC applies to potential vessel scour depths in
Recovery Categories 2 and 3; see Section 10.2. In the intertidal zone for Alternative 5C Plus, all intertidal RALs
must be met to 45 cm depth in Recovery Category 1 areas instead of the top 60 cm for FS alternatives. This is
because 45 cm was deemed by EPA to be sufficiently protective.
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monitoring to determine if surface sediment COC concentrations are reducing overtime as projected by
the natural recovery model. Alternatives with a larger area of ENR and MNR require more long-term
monitoring and maintenance to ensure their effectiveness.
All alternatives rely on institutional controls (ICs) to reduce exposure to contamination remaining after
remediation. Alternatives that rely more on removal of contamination from the waterway through
dredging rely less on institutional controls. Resident seafood consumption advisories are included for all
alternatives; these are informational devices that have historically had limited effectiveness according to
published studies and in EPA's experience. As noted in EPA's EJ Analysis, the community and affected
Tribes have identified several concerns about the use of institutional controls, including the burden placed
on Tribes exercising their treaty rights and on other people who fish in the LDW. To address this concern
to the extent practicable, the EJ Analysis recommends that the affected community and Tribes with treaty
rights be directly involved in advising EPA on institutional controls development, and that enhanced
outreach and education programs be developed for all alternatives. These outreach efforts would include
periodic seafood consumption surveys to identify what species are being eaten by whom, which may
serve as a basis for a more targeted education and outreach program.
Other ICs such as environmental covenants or restricted navigation areas would be employed to protect
caps. Institutional controls in either of these forms regarding ship/vessel use and/or anchoring restrictions
would be used under all alternatives to reduce the possibility of releases of COCs in underlying
sediments. However, these restrictions may be unreliable in much of this heavily used waterway.
Alternative 2R-CAD has the least long-term effectiveness and permanence because it leaves the largest
amount of contamination in place and requires long-term maintenance of a CAD site in the LDW.
Alternatives that leave less subsurface contamination in the waterway are progressively more effective for
this criterion. Alternatives 5C Plus, 5R, 6C,and 6R were the most effective, while other alternatives are
comparatively less effective based on the amount of subsurface contamination left behind.
9.2.2 Reduction of Toxicity, Mobility, or Volume through Treatment
Alternative 5R-Treatment utilizes ex situ soil washing to reduce volumes which would be disposed in a
landfill. The FS assumes that 50% of the ENR area will include in situ treatment (e.g., use of activated
carbon or other amendments) to reduce toxicity and bioavailability. Thus, the reliance on in situ treatment
is proportionate to the amount of ENR. Alternative 6C (with 101 total ENR acres) has the greatest
reliance on ENR (with potential in situ treatment); while 4C (with 16 total ENR acres), and 3C (with 10
total ENR acres) would utilize this technology significantly less. Alternative 5C Plus is in the mid-range,
with 48 total ENR acres. Both in situ and ex situ treatments will require verification and bench or pilot
scale testing during the remedial design phase.
The NCP directs that this criterion also discuss the presence of principal threat waste (PTW) and any
treatment considered for it. PTW is defined in EPA guidance as source material that is highly toxic or
highly mobile, such as pools of non-aqueous phase liquids, and that generally cannot be reliably
contained or would present a significant risk to human health or the environment should exposure occur.
No direct evidence of any significant amounts of non-aqueous phase liquids has been found in LDW
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sediment. EPA has determined that contaminated sediment to be addressed in the LDW by this Proposed
Plan generally is low-level threat waste; however, treatment was included for some alternatives.
Based on these considerations, Alternative 5R-T would provide the most treatment of contaminated
sediment. The "C" alternatives, including 5C Plus, also provide treatment, the degree of which is based on
the amount of area proposed for ENR/in situ treatment.
Alternatives with more dredging and capping provide greater reduction in toxicity and volume of
contaminants in the LDW, although they do not do so by treatment. Dredging, while not considered
treatment under CERCLA, does substantially reduce the toxicity and mobility of contaminants in the
waterway by removing contaminants and placing them in a landfill where they cannot be taken up by fish
and shellfish and be consumed by humans and wildlife. Capping physically and chemically contains
contaminants beneath the cap, thereby reducing mobility and exposure potential.
9.2.3 Short-Term Effectiveness
Short-term impacts associated with the cleanup alternatives may include traffic, noise, air emissions,
habitat disturbance, and elevated fish tissue concentrations during implementation of the cleanup. Local
transportation impacts (traffic, noise, air pollution) from implementation of these alternatives are
proportional to the amount of dredging or the amount of capping, fill, and ENR materials that have to be
transported. Among the technologies evaluated, dredging has the highest potential for short-term impacts
because it takes longer to implement than other technologies, requires transportation of sediments to a
landfill, and creates more disturbance of contaminated subsurface sediments. Short-term impacts
identified in the RI/FS will be evaluated further during remedial design and efforts will be made to
mitigate them and otherwise enhance the environmental benefits of the remedy consistent with CERCLA,
the NCP, and EPA Region 10's Green Remediation policy. For example, impacts due to construction will
be reduced to the extent possible using best management practices and performing in-waterway work
when threatened juvenile salmon are not migrating through the waterway. Dredging often leaves residual
contamination behind; this will be managed by placing a thin layer of clean sand in areas where RALs are
not met after dredging.
EPA's EJ Analysis (Section 9.3.3 and Appendix B) emphasizes the need to reduce risks as quickly as
possible to minimize impacts to the community and Tribes during construction. As recommended by the
EJ Analysis, EPA plans to work with the community and consult with Tribal representatives to reduce
impacts on community and Tribal resources during implementation of the remedy.
Figure 15 describes the construction time and predicted time for each alternative to achieve modeled risk
reduction benchmarks associated with each RAO. These estimates are derived from the time to complete
construction and the natural recovery estimates predicted by the BCM. As discussed in Section 9.1.1, it
was not possible to predict the time to achieve all PRGs. Generally, the potential for short-term impacts
increases as the construction timeframe (based on the area and volume to be actively remediated)
increases. Lower-numbered alternatives, with higher RALs, can be implemented faster than higher-
numbered alternatives with lower RALs. However, lower-numbered alternatives also rely more on natural
recovery and therefore have more uncertainty in their long-term effectiveness.
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Alternatives 5C and 5C Plus provide the best short-term effectiveness by providing the best balance of a
relatively short construction time (7 years) along with a relatively short projected time to reach all cleanup
objectives (17 years). While Alternatives 2R, 3C, 3R, and 4C have shorter construction times, (3-6
years), they are projected to take longer to reach all cleanup objectives (18-24 years) because of the
extended time needed for natural recovery. Alternative 6C is projected to take 16 years to reach all
cleanup objectives, but has a much longer construction time of 16 years. Alternative 6R has a long
construction time and time to reach cleanup objectives of 42 years.
9.2.4 Implementability
Technologies used in these cleanup alternatives have been implemented successfully at other projects in
the Puget Sound region. Alternatives with longer construction times and lower RALs have the potential
for more delays or difficulties. The use of in situ treatment technologies in association with ENR is a
relatively new technology in the Puget Sound region and will require pilot testing before full
implementation. The soil washing component of Alternative 5R-Treatment has potential technical and
administrative challenges associated with locating and permitting an upland soil washing facility, and
potentially with reuse or disposal of treated material. Treatability studies would be required to verify the
suitability of soil washing as a viable treatment technology.
Alternatives with higher RALs and larger MNR footprints have a higher potential for requiring additional
actions if MNR To SQS does not reduce contaminant concentrations as expected. This may cause an
additional administrative burden to determine specific additional actions, and to provide oversight during
implementation of such actions. Alternative 2R-CAD has a potentially significant administrative
challenge related to locating, using, and maintaining one or more CAD facilities.
Institutional controls are an expected requirement of all remedial alternatives to manage human health
risks from resident seafood consumption. The primary control mechanisms are seafood consumption
advisories, public education and outreach, and environmental covenants pursuant to the Washington
Uniform Environmental Covenants Act. This Act extends statutory enforcement rights to both EPA and
Ecology. However, these controls can be difficult to monitor. Seafood consumption advisories are not
enforceable, and have limited effectiveness. For these reasons, alternatives that rely less on institutional
controls are more readily implementable.
Alternatives 5R, 5R-T, 6R, and 2R-CAD have the greatest potential implementability challenges due to
the long construction timeframes for 5R and 6R and the difficulties associated with building and
operating a soil washing technology (5R-T) or a CAD site (2R-CAD). Alternatives 4C, 4R, 5C, and
5C Plus are all similarly highly implementable because they rely on technologies that have been proven
effective at other cleanups and are administratively feasible, and their large actively remediated areas
equate to a low probability for triggering additional actions in the future.
9.2.5 Cost
Thirty-year net-present value costs for each alternative, calculated with a 2.3% discount rate, are provided
in Table 12. The estimated cost of $305 million for Alternative 5C Plus falls within the low end of the
cost range for the FS alternatives ($200 million - $810 million).
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9.3 Modifying Criteria
Modifying Criteria are considered to the extent that information is available during the FS, but will be
fully considered only after public comment is received on the Proposed Plan. The findings and
recommendations in EPA's EJ Analysis (Appendix B) were also considered as part of the two modifying
criteria.
9.3.1 Community Acceptance
Community acceptance of the preferred remedy will be assessed in the ROD based on public comments
received on this Proposed Plan. However, EPA and Ecology have provided opportunities for comment
throughout the RI/FS process, including informal public comment periods on the RI and FS Reports.
More than 300 letters were received from individuals, businesses, interest groups, Tribes, and government
agencies during a 2010 informal public comment period on the FS. Concerns raised during the FS
comment period included:
• The importance of reducing pollution entering the LDW to avoid new contamination and to help keep
cleaned-up areas from becoming contaminated again (i.e., source control).
• Concern about the cost of the cleanup and who will pay for it.
• Concern that cleanup of the LDW is not anticipated to achieve contaminant concentrations that would
allow people to eat an unrestricted amount of resident fish and shellfish.
• A desire for flexibility in cleanup decision-making.
• A request for an environmental justice analysis to identify vulnerable communities affected by the
cleanup, and how these communities will be affected by each of the alternatives.
9.3.2 State/Tribal Acceptance
EPA and Ecology co-issued the RI/FS Consent Order for the LDW, and oversaw its implementation
together. Ecology supports the Preferred Alternative, and EPA supports Ecology's Source Control
Strategy (Appendix A). Tribal acceptance will be determined following government-to-government
consultation with The Muckleshoot and Suquamish Tribes, consistent with EPA policy.
Community and Tribal concerns were also considered during the development of EPA's EJ analysis,
discussed below. EPA will evaluate State, Tribal, and community acceptance of the Preferred Alternative
following the public comment period on this Proposed Plan.
9.3.3 Environmental Justice Analysis
EPA's EJ Analysis examined the impacts of the Preferred Alternative and other FS alternatives on those
who subsist on, work in, and play in the LDW. The EJ analysis considered the potential for
disproportionate adverse impacts from the FS alternatives and the Preferred Alternative on the community
and affected Tribes, particularly those who consume resident fish and shellfish or have contact with LDW
sediments. In the EJ analysis, the cleanup alternatives were compared qualitatively for their long-term and
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short-term residual cancer and non-cancer risks; the time to achieve human health targets; the certainty of
the methods used to conduct the cleanup; and the dependence upon institutional controls which have
implications for environmental justice concerns on behalf of the affected community. EPA's EJ Analysis
determined that the Preferred Alternative balances the need to reduce human health risks quickly while
providing certainty that the methods used in cleanup will be effective and will remain effective in the
future. It also recommended additional measures to mitigate adverse disproportionate impacts. The EJ
Analysis lists the following recommendations:
1. Emphasize reduction of greatest human health risks as soon as possible while ensuring that cleanup
methods used will be effective and last over the long-term;
2. Form and fund an advisory group with support for local community outreach experts to meaningfully
involve the community in developing the most appropriate mitigations for exposure from eating
resident seafood at the Site;
3. Continue support for Tribal consultation, participation, and early involvement;
4. Support a local fisher consumption survey specific to the LDW (to find out where, when, and what
they are fishing for to provide critical information in the development of institutional controls, offsets,
and enhanced education)12;
5. Establish a mechanism to provide offsets in the event of higher short-term concentrations in fish
tissue in the LDW: fish trading may be the most straightforward, but there would be cost savings
potentially through a sustainable aquaculture or alternative transportation method; offsets for Tribes
to be developed in consultation;
6. Use green remediation techniques, such as technologies that reduce air impacts, with any cleanup
alternative chosen.
9.4 Summary of CERCLA Evaluation
Alternative 1 is not protective and cannot achieve ARARs; it is eliminated from further consideration.
Alternatives 2 to 6 rely on MNRto varying degrees. They are protective and are projected by RI/FS
models to provide substantial risk reduction. All Alternatives also rely on seafood consumption
advisories as institutional controls to limit seafood consumption to protect human health. These
Alternatives can also meet ARARs, although whether the Preferred Alternative, in conjunction with
source control, can achieve all human health PRGs is uncertain.
Alternative 2R-CAD provides the least long-term effectiveness and permanence because it requires long-
term maintenance of a CAD site within the waterway and leaves the most subsurface contamination in
place. The removal-emphasis alternatives, 2R through 6R, leave progressively less subsurface
contamination in place that could be exposed by vessel scour or earthquakes, and require fewer use
restrictions and less maintenance. They also have comparatively longer construction times and are more
12. EPA has already started to implement this recommendation as part of the RI/FS.
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expensive than combined ("C") alternatives with similar RALs. The combined alternatives, 3C through
6C, and especially the lower-numbered combined alternatives, have more area managed by ENR and
MNR (and thus more subsurface contamination left in place), and have greater monitoring and
maintenance requirements. Alternative 5C Plus adds to Alternative 5C an increased emphasis on removal
of high levels of PCBs in shallow subsurface sediments, providing greater permanence. Under 5C Plus,
MNR is allowed in areas with moderate to low concentrations of non-human health COCs to allow for a
moderate construction time and to shorten the overall time to achieve cleanup objectives. While
Alternatives 5R, 6C and 6R remove more subsurface contamination, they disrupt the waterway over a
much longer construction period, and at a considerably higher cost than 5C Plus (Table 13).
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10 EPA's Preferred Alternative
After consideration of the remedial alternatives presented in the 2012 Feasibility Study, the 2012 FS
Supplement, and in consultation with the State of Washington and Muckleshoot and Suquamish Tribes,
EPA proposes Alternative 5C Plus (Scenario 5a in the FS Supplement), as the Preferred Alternative for
the in-waterway portion of the Site.
The Preferred Alternative may change in response to public comments or if new information becomes
available that would influence remedy selection. Any changes (below the threshold requiring another
public comment period) will be identified in the ROD and discussed further in the Responsiveness
Summary.
Section 10.1 provides a brief description of the Preferred Alternative, and Section 10.2 provides details
about how RALs, PRGs, and Recovery Categories were used to identify the areas in which specific
technologies were applied, and how they will be used to refine these areas during remedial design.
Section 10.3 provides EPA's rationale for selecting the Preferred Alternative.
10.1 Description of the Preferred Alternative
Figure 18 shows the areas of contaminated sediments that would be remediated under Alternative 5C
Plus. Figure 19 and Figure 20 describe how remedial technologies were applied to the RI/FS sediment
data to develop the map in Figure 18. The PRGs EPA is proposing to select as cleanup levels in the ROD
are described in Section 7. The RALs for the Preferred Alternative are shown in Table 12 and Table 14.
The Preferred Alternative addresses all areas where contaminant concentrations exceed the PRGs through
a combination of active cleanup technologies, monitored natural recovery, and institutional controls. It
consists of the following elements:
Apply active cleanup technologies in a total of 156 acres:
• Dredge or partial-dredge and cap approximately 84 acres of more highly contaminated sediments (see
Section 10.2) where it is necessary to maintain water depth for human use or to maintain habitat.
Approximately 790,000 cubic yards of dredged materials will be transported via truck or rail for
disposal at a permitted upland off-site landfill facility.13 If sediment contamination is 4 feet thick14 or
less in an area selected for dredging, all contaminated sediments will be dredged. If contamination is
greater than 4 feet thick, sediments will be partially dredged and capped.
• Place engineered sediment caps on approximately 24 acres of more highly contaminated sediments
where there is sufficient water depth for a cap.
13. Some clean materials may be dredged as part of the cleanup; for example, in order to maintain appropriate
sideslopes at the edge of a dredge cut. Clean sediments that pass the Dredged Materials Management Program's
criteria may be disposed at an open-water disposal site.
14. The 4-ft thickness for dredging is based on an FS evaluation that it is cost-effective to dredge all contaminated
sediments when the contamination thickness is 4 ft or less, but at a thickness of greater than 4 ft, it is more cost-
effective to partially dredge the contaminated sediments then construct a cap to isolate the remaining contamination.
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• Place a thin layer (6 to 9 inches) of clean material (referred to as enhanced natural recovery [ENR]) in
approximately 49 acres of sediments in areas that meet the criteria for ENR (Figure 19 and Figure
20). Suitable habitat materials will be used in habitat areas. ENR may include in situ treatment using
activated carbon or other amendments, and engineered designs for sediment stability. The
effectiveness and potential impacts of using in situ treatment or amendment technologies, as well as
the areas best suited for these technologies, will be evaluated in pilot studies performed during
remedial design.
• Maintain sufficient water depth for human use and habitat function through application of the
following criteria:
- All areas above -10 ft MLLW are considered habitat areas, and will be maintained at their current
elevation and backfilled or capped with suitable habitat materials.
- The Federal navigation channel and berthing areas will be maintained at or below their current
operating depths. In order to avoid damage to a cap or ENR layer during maintenance dredging,
the top of any ENR layer will be at least 2 ft and the top of any cap will be at least 3 ft below the
authorized Federal navigation channel depth (2 ft below the operating depth for berthing areas).
Shoaled areas in the navigation channel (where the bottom elevation is currently shallower than
the navigation depth) will be dredged if COCs in the top 2 ft of sediments exceed the RALs.
• Remove debris and pilings throughout the LDW as necessary or as required by EPA to implement the
remedy, and dispose of materials at a permitted off-site facility.
Implement monitored natural recovery (MNR) in approximately 256 acres of sediments where
surface sediment contaminant concentrations are predicted to be reduced over time through deposition of
cleaner sediments from upstream. MNR will apply to those areas that are not subject to active
remediation, using either MNR To SQS or MNR Below SQS, as described below. The STM and BCM,
supported by data collected during the RI/FS, were used to estimate the amount of time required to reduce
COC concentrations in sediments through natural recovery. For all areas where MNR is applied, long-
term monitoring of surface sediments (top 10 cm) will be implemented to evaluate whether the PRGs for
protection of benthic invertebrates (the SQS) are being achieved in a reasonable timeframe or are not met
within 10 years after remediation.
• In MNR areas, more intensive long-term monitoring will be conducted in areas with sediment COC
concentrations that are less than sediment RALs but greater than the SQS (referred to as MNR To
SQS).
• Should MNR not achieve SQS or progress sufficiently toward achieving it in 10 years, additional
cleanup (e.g., dredging, capping, or ENR, following the decision criteria in Figure 19 and Figure 20)
will be required.
• Less intensive monitoring will be conducted in areas with sediment COC concentrations that are
below the SQS but above the sediment PRGs for protection of human health (referred to as MNR
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Below SQS). If these PRGs are not achieved, additional cleanup actions will be considered in a future
decision document.
• Sample the entire LDW (441 acres) as part of baseline, construction, post-construction, and
long-term monitoring - Conduct sampling and analysis to establish post-EAA cleanup baseline
conditions during remedial design, including surface and subsurface sediments, surface water, and
fish and shellfish tissue.
- Remedial design sampling data will be used to modify the cleanup footprint shown in Figure 18.
Sampling data will be compared to sediment RALs for intertidal and subtidal areas in Figure 21
and Figure 22, and as described in Section 10.2.
Remedial design data will also be analyzed to evaluate of the effectiveness of EAA cleanups and
natural recovery that have occurred since the RI/FS sampling and to serve as a baseline for
comparison to post-cleanup data.
- If any sediment COC concentration at any location exceeds its contaminant-specific RAL for a
specified interval, then active remediation (dredging, capping, or ENR, or a combination thereof)
will be required.
- The type of remedial technology to be applied will be consistent with remedial technology
applications shown in Figure 19 and Figure 20. Area-specific technologies will be selected for
areas with structural or access limitations (e.g., under piers).
• Conduct research during remedial design to further assess the relationship between arsenic and cPAH
concentrations in sediment and clam tissue, and to assess whether remedial action can reduce clam
tissue concentrations to the PRGs. EPA anticipates that source control and the proposed remedial
actions in the Preferred Alternative will lower clam inorganic arsenic and cPAH concentrations;
however, the amount of reduction is unknown. If EPA determines, based on these studies, that
additional remedial action is needed to achieve clam tissue cleanup levels, this decision will be
addressed in a future decision document.
• Conduct environmental compliance monitoring during construction, as well as monitoring during and
after construction, to ensure compliance with construction standards and project design documents.
• Conduct post-construction and long-term monitoring for sediments, surface water, fish and shellfish
tissue, and other media as determined during remedial design to ensure protectiveness of human
health and the environment and to protect the integrity of the remedial actions and aid in the
evaluation of source control effectiveness. A subset of baseline and long-term monitoring samples
will be analyzed for other contaminants not selected as COCs but identified in the HHRA as posing
an excess cancer risk of greater than 1 in 1,000,000 or non cancer HQ of 1 at the adult Tribal RME, to
assess their reduction overtime.
Provide institutional controls (ICs) for the entire waterway to reduce exposure to contaminants,
ensure remedy protectiveness, and protect the integrity of the remedy, while minimizing reliance on ICs,
particularly seafood consumption-related ICs, to the extent practicable. ICs will include proprietary
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controls in the form of environmental covenants pursuant to the Washington Uniform Environmental
Covenants Act (UECA), and informational devices including fish and shellfish consumption advisories to
reduce human exposure from ingestion of contaminated resident seafood. EPA will rely on the existing
WDOH fish and shellfish consumption advisories (see Seafood Advisories for the Lower Duwamish
Waterway, page 14) and may implement additional advisories or other measure to provide additional
protectiveness. Outreach and education programs will also be used to enhance seafood consumption
advisories.
Cost of the Preferred Alternative - The total estimated capital costs (net present value) to construct the
Preferred Alternative are $258 million, and the total estimated operation, maintenance, and monitoring
costs (net present value) are approximately $47 million for a total of $305 million (excluding the cost of
source control, which is not part of the in-waterway portion of the Site, and the cost of the Early Actions).
The Preferred Alternative is estimated to take 7 years to construct.
Role of EAAs in the Preferred Alternative - The remedial technologies described above for the
Preferred Alternative apply to 412 acres of the LDW. An additional 29 acres of the most contaminated
sediments in the LDW have been or will be addressed by cleanups in Early Action Areas (described in
Sections 2.1 and 5.1). EPAhas reviewed the EAA cleanup actions subject to implementation under EPA
Consent Orders (Slip 4, Terminal 117, and Boeing Plant 2/Jorgensen Forge), and has determined that the
completed Slip 4 EAA is consistent with the Preferred Alternative and requires no further active
remediation, and other planned EAAs are similarly expected to require no further active remediation if
they achieve their stated objectives. For the cleanups conducted under the 1991 Natural Resource
Damages Consent Decree (Norfolk CSO and Duwamish/Diagonal CSO/SD), EPA will conduct a review
during the remedial design phase to determine whether additional work is needed to make these cleanup
actions consistent with the remedy selected in the ROD. EPA will review the ICs Plans and long-term
monitoring plans for all of the EAAs and will require that the EAAs be incorporated into plans for the rest
of the LDW as necessary to make them consistent with the remedy selected in the ROD.
Role of Source Control in the Preferred Alternative - The Selected Remedy will be implemented
while a comprehensive source control program is managed by Ecology, as originally described in the
2004 Source Control Strategy and further defined in the 2012 Source Control Strategy (Appendix A).
EPA and Ecology will coordinate to their respective work as lead agencies to maximize consistency and
ensure that sources have been sufficiently controlled to minimize recontamination before initiating
sediment cleanup in any portion of the waterway. The coordination process will be further developed in a
new Memorandum of Understanding (MOU) (replacing a 2004 MOU), which the Agencies expect to
execute prior to issuance of the ROD for the in-waterway portion of the Site.
This Proposed Plan addresses EPA's in-waterway cleanup only and does not limit the laws and
regulations Ecology uses to implement source control as detailed in Appendix A. In addition, Ecology
may require sampling and control of additional contaminants beyond those listed as COCs in this
Proposed Plan to address the goals and objectives of the source control program.
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10.2 Implementation of the Preferred Alternative
The estimates of areas, volumes, time to reach cleanup objectives, and cost described in Section 10.1 are
based on RI/FS data. Remedial design sampling will be conducted after the early actions are completed in
2015. Results from design sampling will be used by EPA to refine areas to be remediated and the
remediation technologies to be applied, and inform source control activities.
This section describes how future data will be used to refine the areas where each technology will be
applied. RALs will be applied in intertidal and subtidal areas to identify areas for active remediation as
described below and in Figure 21 and Figure 22. The type of remedial technology to be applied to
sediments is described below and in Figure 19 and Figure 20.
In Recovery Category 1 areas, (approximately 11 intertidal acres and 66 subtidal acres), active
remediation (dredging, capping, or a combination thereof) is required when:
• Any sediment COC concentration in the top 10 cm is greater than the ecological RALs (SQS) or
greater than the four human health RALs (PCBs, arsenic, cPAHs, dioxins/furans) in intertidal and
subtidal areas.
• Sediment COC concentrations averaged over the top 45 cm in intertidal areas are greater than any of
the four human health RALs.
• Sediment COC concentrations averaged over the top 60 cm in subtidal areas are greater than any of
the SQS RALs or greater than any of the four human health RALs.
• ENR will not be applied to Recovery Category 1 areas.
In Recovery Category 2 and 3 areas (approximately 102 intertidal and 233 subtidal acres), active
remediation (dredging, capping, ENR, or a combination thereof) is required:
• In intertidal and subtidal areas, when any sediment COC concentration in the top 10 cm is greater
than 2 times the SQS or the CSL, whichever is lower (Table 14) or is greater than any of the four
human health RALs.
• In intertidal areas, when sediment COC concentrations averaged over the top 45 cm are greater than
any of the human health RALs for arsenic, cPAHs, or dioxins/furans, or when PCB sediment
concentrations are greater than the CSL.
• In subtidal areas at depths above potential vessel scour depths15 (approximately 128 acres), when
sediment PCB concentrations averaged over the top 60 cm are greater than 3 times CSL (195 mg/kg
OC) for PCBs . There are no RALs for the top 60 cm in Category 2 and 3 areas in deeper water
depths (105 acres).
15. Subtidal areas in Recovery Categories 2 and 3 deemed to be potentially subject to vessel scour especially by
tugboats are: north of the 1st Avenue South Bridge (located at approximately RM 2) in water depths from -4 to -24
ft MLLW, and south of the 1st Avenue South Bridge, in water depths from -4 to -18 ft MLLW. These depths are
based on the size of tugboats that normally operate in these areas.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
ENR with or without in situ treatment will be selected based on sediment COC concentrations and the
potential for sediment scour at certain water depths, as discussed below:
• In intertidal areas in Recovery Categories 2 and 3, ENR will be applied when any sediment COC
concentration in the top 10 cm is between 1 and 3 times the top 10 cm intertidal RALs , or when any
sediment COC concentration averaged over the top 45 cm is between 1 and 1.5 times the intertidal
RALs for the 45 cm interval (e.g., 65 - 97 mg/kg OC PCBs) (Figure 21 and Table 14).
• In Recovery Category 2 and 3 subtidal areas, ENR will be applied when any sediment COC
concentration in the top 10 cm is between 1 and 3 times the top 10 cm subtidal RALs as noted in
Figure 20 and Table 14. In potential vessel scour areas, PCB concentrations in the top 60 cm must
also be less than 3 times the CSL.
• Pilot testing will be performed in the remedial design phase to develop criteria for determining
whether ENR/in situ treatment is effective in reducing toxicity and bioavailability of COCs while
avoiding unacceptable impacts to biota. The results of pilot testing will determine the locations where
in situ treatment will be applied. If pilot testing is successful, EPA will consider, in coordination with
the State, Tribes, and stakeholders, expanding the area to which ENR/in situ treatment may be
applied.
• Areas not suitable for ENR will be remediated by dredging, capping, or partial dredging and capping,
as described in Figure 19 and Figure 20.
In all other areas of the LDW, MNR will be applied as follows:
• In areas with concentrations of COCs at or below the Alternative 5C ecological risk reduction RALs
(2 times the SQS or the CSL, whichever is lower [Table 14]), MNR To SQS will be used to reduce
COC concentrations to the SQS so long as the human health RALs are not also exceeded. If the SQS
is not reached in 10 years after remediation, additional remedial action will be required.
• In areas where COC concentrations are below the SQS, MNR Below SQS will further reduce COC
concentrations in sediments after active remediation is complete.
10.3 Rationale for Identification of 5C Plus as the Preferred
Alternative
The Preferred Alternative is recommended because it is protective of human health and the environment,
and provides the best balance of tradeoffs among the balancing criteria. It reduces risks within a
reasonable time frame, is practicable and cost-effective, provides for long-term reliability of the remedy,
and minimizes reliance on institutional controls. It will achieve substantial risk reduction by dredging and
capping the most contaminated sediments, reduce remaining risks to the extent practicable through ENR
and MNR, and manage remaining risks through institutional controls. This combination provides the best
balance of construction time, long term effectiveness and permanence, time to achieve risk reduction, and
cost.
In selecting 5C Plus as the Preferred Alternative, EPA considered several options for surface and
subsurface RALs. EPA selected the RALs listed in this Proposed Plan because other options removed
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Proposed Plan — Lower Duwamish Waterway Superfund Site
less subsurface contamination with an associated increased risk of exposure, or removed more subsurface
contamination at a higher cost that was disproportional to the increase in long-term effectiveness and
permanence. More than other alternatives, Alternative 5C Plus emphasizes removal of PCB
contamination in shallow subsurface sediments while allowing MNR in areas with low concentrations of
non-human health COCs, providing greater permanence in comparison to other alternatives of similar cost
and construction duration. Less costly alternatives rely more on technologies such as ENR and MNR that
have uncertainty as to their long-term effectiveness. In more costly alternatives, the additional costs are
not proportional to the overall increase in protectiveness. Alternative 5C Plus provides the best balance of
minimizing short-term risks due to construction in a 7-year construction period, while maximizing long-
term effectiveness by dredging or capping the most contaminated sediments. The Preferred Alternative
will utilize treatment to reduce the toxicity and bioavailability of contaminants in the form of ENR with in
situ amendments if pilot testing is successful. It is consistent with current and reasonably anticipated
future uses of the waterway.
Addressing Environmental Justice concerns - Environmental Justice concerns will be addressed
before, during and after implementation of the remedy by:
1. Proposing a Preferred Alternative that reduces human health risks as quickly as possible, while also
providing for long-term effectiveness and permanence.
2. Conducting surveys to learn more about the affected community (those who consume Duwamish
resident seafood) in order to enhance outreach efforts. As noted in Section 9.3.3, EPA has already
started implementing this recommendation as part of the RI/FS.
3. Continuing to engage the community throughout remedial design and implementation of the cleanup,
including convening an advisory group as a means for the affected community and local agencies to
work together on mitigating the impacts of the cleanup on the affected community.
4. Continuing consultation with affected Tribes on recommendations for the remedy.
5. Reducing the impacts of the cleanup on residents through green remediation techniques.
Attaining ARARs - The intent of the Preferred Alternative is, in conjunction with cleanup of the EAAs
and source control activities described in the attached 2012 Source Control Strategy, to be protective of
human health and the environment and to attain ARARs, although some ARARs may not be achieved for
many years. It is intended to minimize reliance on seafood consumption-related Institutional Controls to
the extent practicable.
The goal of this CERCLA cleanup action and Ecology's source control program is to reduce in-waterway
contamination and sources to the waterway to levels needed to achieve all ARARs-based and risk-based
cleanup levels in the ROD. EPA acknowledges that the RI/FS modeling results conclude that it may not
be possible for any alternative to do so; however, as discussed in Sections 7 and 9, it is difficult to predict
long-term Site conditions with any degree of accuracy. Model results are based on current Site
conditions, and do not take into account potential future advances in technologies for addressing
contamination in urban waterways.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
EPA will review long-term monitoring data to assess the success of the remedy, including measuring
contaminant concentrations in sediment, surface water, and fish and shellfish tissue. If long-term
monitoring data show that any SQS (Table 9) are exceeded, additional actions will be taken to reduce
COC concentrations to the SQS. If monitoring data reach a steady state at levels below the SQS but
above the human health risk reduction or background-based cleanup levels in the ROD, EPA will review
the data and consider whether additional sediment cleanup has the potential to further reduce COC
concentrations in sediments, tissue, or surface water and associated human health risk and is technically
practicable. If so, EPA, in consultation with Ecology and the Suquamish and Muckleshoot Tribes, will
select additional remedial action in a future decision document (ROD Amendment or ESD). If EPA
determines that no additional practicable actions can be implemented to meet ARARs, EPA may issue a
Proposed Plan for a ROD Amendment or ESD providing the basis for a technical impracticability waiver
for specified sediment and/or water quality-based ARARs under Section 121(d)(4)(C) of CERCLA and
including an opportunity for public comment as appropriate.
Whether ARARs are attained or not, implementation of the Preferred Alternative, along with the EAAs
and source control, will substantially improve the quality of LDW sediments and surface water, reduce
COC concentrations in waterway organisms, and result in an estimated 90% or greater reduction in
seafood consumption risk .
10.4 Preferred Alternative Summary
Based on the information currently available, the Preferred Alternative described in this Proposed Plan is
a final action which meets the threshold criteria and provides the best balance of tradeoffs with respect to
the balancing and modifying criteria. EPA expects the Preferred Alternative to satisfy the following
statutory requirements of CERCLA § 121(b): 1) be protective of public health and the environment;
2) attain ARARs; 3) be cost-effective; 4) utilize permanent solutions and alternative treatment (or
resource recovery) technologies to the maximum extent practicable; and 5) satisfy the preference for
treatment as a principal element, or explain why the preference for treatment will not be met.
Ecology supports the Preferred Alternative , and EPA supports Ecology's Source Control Strategy
(Appendix A).
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Proposed Plan — Lower Duwamish Waterway Superfund Site
0 200 400
Legend
Technology Assignment
Dredge (64 acres)
m Partial Dredge and Cap (20 acres)
Cap (24 acres)
| ENR/in situ (48 acres)
| Monitored Natural Recovery (Surface Sediment >SQS)(33 acres)
Monitored natural recovery (surface sediment -4 ft MLLW
---- Navigation Channel
River Mile Marker
Figure 18. Preferred Alternative
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Box 1. Intertidal Sediments (+11.3 ft MLLW to -4 ft MLLW)
Remedial Action Levels (RALs) and Vertical Point of Compliance ("Depth lnterval")-Footnote 2
Recovery Category 1 Areas
Recovery Category 2 and J Areas
4 in (10 cm)
1.5 ft (45 cm)
4 in (10 cm)
1.5 ft (45 cm)
Contaminant
Units
depth interval
depth interval
depth interval
depth interva
Risk Drivers
PCBs (Total)
mg/kg-OC
12
12
12
65
Human Health
Footnote 3
Risk Reduction 3 c,!:
cPAH
TEQ ug/kg-dw
1000
900
1000
900
Dioxins/Furans
ngTEQ/kg-dw
25
28
25
28
Arsenic (Total)
mg/kg-dw
57
28
57
28
41 SMS Chemicals'
SQS*
--
2xSQSe,t
--
Ecological Risk
Reduction3
Notes:
The average concentrations in depth interval (e.g., vertically composited samples) are compared to RALs.
RALs Must Be Met Immediately Following Construction.
4RAO 1- Human Heafth Seafood Consumption
6 RAO 2 - Human Health Direct Contact is Beach P;ay, Clamming, and Netfishing
5 RAO 4 - Ecological Protection for River Otter (Addressed by Meeting Human Health PCB RAL)
= RAO 3 - Ecological Protection of Benthic Community
'Washington State Sediment Management Standards (SMS) Sediment Qua1 ity Standards (SQS) for 41 contaminants are shown in
Tabie 7; the SMS Also Lists Toxicity Test-out Criteria for Bioassays. Test-out is not allowed for the 4 human hea!th risk driver COCs.
f RAL is "2xSQS and not to exceed CSL
" i his RAL is for 39 SQS , which exciudes the two SQS COCs that are human health COCs (PCBs
and Arsenic)
Legend:
Monitored Natural Recovery
(Active Remedial Technology
Application
All Remedial Technologies Include
Long-Term Monitoring and
Institutional Controls
Box 2. Habitat Area Restoration
Elevations of Intertidal Habitat Areas are Assumed to be Unaffected by Addition of 6-9" Materials (i.e., ENR)
Dredge and Backfill or Partial Dredge and Cap to Pre-Construction Grade; Finish with Suitable Habitat Layer
In Clam Habitat areas (Proposed Plan Figure 4), Minimum of 4 ft of Suitable Clean Material Including a Surface Suitable
for Clam Growth
Footnotes:
1) For concentrations less than SQS, should further remedial action be required, they will be the subject of a new decision document.
2) See Figure 23, which shows the application of RALs in intertidal areas.
3) The FS used 240 ppb PCBs (dry weight equivalent of 12 ppm-OC PCB at 2% organic carbon content) for mapping purposes.
Definition: Remedial Action Levels (RALs) are contaminant-specific sediment concentrations designed to address human health and ecological risk and to trigger the
need for active remediation.
Abbreviations: COC - risk driver contaminant of concern; cPAH - carcinogenic polynuclear aromatic hydrocarbons; ENR - Enhanced Natural Recovery; MLLW - mean
lower low water; RAL - remedial action level; RAO - remedial action objective; PCB - polychlorinated biphenyls; SQS - Sediment Quality Standards, TEQ - toxicity
equivalents: for dioxins/furans TEQ is expressed as 2,3,7,8-Tetrachloro-p-dibenzodioxin equivalents; for cPAHs, TEQ is expressed as benzo[a]pyrene equivalents
Figure 19. Intertidal Areas - Remedial Technology Applications
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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Proposed Plan
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Monitored Natural Recovery \
(See Footnote 1) I
Area-Specific Technology
(e.g., Cap Shallower than 3 ft)
< Enhanced Natural Recovery \
(With or Without In-Situ Treatment) J
Partial Dredge and Cap
(See Box 2)
Dredge
(See Box 2)
Cap or Armored Cap
(See Box 2)
Box 1. Subtidal Sediments (-4 ft MLLW and Deeper)
Remedial Action Levels (RALs) and Vertical Point of Compliance ("Depth lnterval")-Foofr)ofe 2
Recovery Category 1 Areas
Recovery Category 2 and } Areas
2 ft (60 cm) depth
interval (applied only
4 .n (10 cm) depth
2 ft (60 cm) depth
4 in (10 cm) depth
at potent'a' tug scour
Contaminant
Units
interval
interval
interval
areas) Footnote g
Risk Drivers
PCBs (Total)
mg/kg-OC
12
12
12
195
Human Health
Footnote 3
Risk Reduction
cPAH
TEQ ug/kg-dw
1000
1000
1000
—
Dioxins/Furans
ngTEQ/kg-dw
25
25
25
—
Arsenic (Total)
mg/kg-dw
57
57
57
-
41 SMS Chemicals e
SQS5
SQSe
2xSQS"f
—
Ecological Risk
Reductionc
Notes
The average concentrations in depth interval (e.g., vertically composited samples) are compared to RALs.
Potential tug scour areas are subtidal elevations potentially susceptible to propellor wash (shallower than-24 ft MLLW north of 1st
Ave Bridge and shallower than-18 ft MLLW north of 1st Ave Bridge at RM 2.0). Below these water depths, no RAL is employed in the
50 cm depth interval.
RALs Must Be Met Immediately Following Construction.
s RAO 1 - Human Health Seafood Consumption
° RAO 2 - Human Health Direct Contact is Beach Play, Clamming, and Netfishing
: RAO 4 - Ecological Protection for River Otter (Addressed by Meeting Human Health PCB RAL)
0 RAO 3 - Ecoiogica' Protection of Benthic Community
'Washington State Sediment Management Standards (SMS) Sediment Quality Standards (SQS) for 41 contaminants are shown in
Table 7; the SMS Also Lists Toxicity Test-out Criteria for Boassays, Test out is not ai lowed for the 4 human health risk driver COCs.
' RAL is "2xSQS and not to exceed CSL" This RAL is for 39 SQS , which excludes the two SQS COCs that are human health COCs (PCBs and Arsenic)
Legend:
Monitored Natural Recovery
Active Remedial Technology \
Application j
All Remedial Technologies Include
Long-Term Monitoring and
Institutional Controls
Box 2. Habitat Areas (Shallower than -10 ft MLLW and Excluding Engineered Slopes, Riprap, or Berthing Areas)
Elevations of Intertidal Habitat Areas are Assumed to be Unaffected by Addition of 6-9" Materials (i.e., ENR)
Dredge and Backfill or Partial Dredge and Cap to pre-Construction Grade; Finish with Suitable Habitat Layer
Footnotes:
1) For concentrations less than SQS, should further remedial action be required, they will be the subject of a new decision document .
2) See Figure 24, which shows the application of RALs in subtidal areas.
3) The FS used 240 ppb PCBs (dry weight equivalent of 12 ppm-OC PCB at 2% organic carbon content) for mapping purposes.
Definition: Remedial Action Levels (RALs) are contaminant-specific sediment concentrations designed to address human health and ecological risk and to trigger the need for
active remediation.
Abbreviations: COC - risk driver contaminant of concern; cPAH - carcinogenic polynuclear aromatic hydrocarbons; ENR - Enhanced Natural Recovery; MLLW- mean lower
low water; OC - organic carbon, RAL - remedial action level; RAO - remedial action objective; PCB - polychlorinated biphenyls; SQS - Sediment Quality Standards; TEQ -
toxicity equivalents: for dioxins/furans TEQ is expressed as 2,3,7,8-Tetrachloro-p-dibenzodioxin equivalents; for cPAHs, TEQ is expressed as benzo[a]pyrene equivalents
Figure 20. Subtidal Areas - Remedial Technology Application
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Proposed Plan — Lower Duwamish Waterway Superfund Site
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Proposed Plan — Lower Duwamish Waterway Superfund Site
+11.3 ft to -4 ft MLLW: 113 acres a
Depth Interval:
Remedial Action Levelsf:
Depth Interval:
Remedial Action Levels:
Mudline
4 in
(10cm)'-
1.5 ft
(45cm)r
Sediment
coc
> 41 SQS
Sediment
COC
> 4 Human Healti
(apply site-wide)
•12 mg/kg OCPCB"
•57 mg/kg dw Arsenic
•1,000 pg TEQ/kg dwcPAH
*25 ng TEQ/kg dw Dioxins/ Furans
> 4 Human Health
(apply only in intertidal)
•12 mg/ kg OC PCBd
•28 mg/ kg dw Arsenic
•900 |ig TEQ/kg dw cPAH
• 28 ng TEQ/kg dw Dioxins/ Furans
Notes:
>
O
r+
<"
a>
xi
CD
fD
Q.
Qj'
rt-
o'
d
cr
Mudline
4 in
(10cm)
1.5 ft
(45cm)
J
Sediment
COC
> 39 SMS at 2x SQSe
> 4 Human Health
(apply site-wide)
Sediment
COC
•12 mg/kg OC PCBC
•57 mg/kg dw Arsenic
•1,000 [ig TEQ/kg dwcPAH
•25 ng TEQ/kg dw Dioxins/ Furans
> 4 Human Health
(apply only in intertidal)
¦65 mg/kg OC PCB
•28 ug/kg Arsenic
•900 |ig TEQ/kg dw cPAH
¦28 ng TEQ/kg dw Dioxins/ Furans
a) 113 intertidal acres excludes 15 intertidal acres in Early Action Areas.
b) Clam Habitat Areas that are dredged or capped must have a minimum of 4 ft clean cap material. COC = Risk Driver Contaminant of Concern
c) Active remediation= dredge, partial dredge and cap, or ENR. See remedial technology applications In flowcharts in Figures 18a and b. SQS = Washington Sediment Quality Standard
d) The dry weight equivalent of this RAL (240 pg/kg dw PCS assuming 2% organic carbon ) was used In the FS for mapping purposes, OC - organic carbon
e) RAL is "2XSQS and not to exceed CSL." This RAL for surface sediments would only be used for 39 of the 41 SQS COCs, and would not be used for any of the four human health risk driver COCs (PCBs, arsenic,
cPAH, and dioxins/furans). If SQS is not met 10 years after remedial action, contingency actions may be needed.
f) Example: In Category 1, if any sediment COC concentrations in the top 10 cm are greater than the 41 SQS RALs, then active remediation is required. Also, if any COCs in the top 10 cm are greater than the
four HH RALs, then active remediation is required.
Figure 21. Intertidal Areas - Remedial Action Levels Application
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Proposed Plan — Lower Duwamish Waterway Superfund Site
-4 ft MLLW and Deeper: 299 acres
Recovery Category 1 (66 Acres)
Natural Recovery of Sediments Predicted to be Limited
Recovery Categories 2 and 3 (233 Acres)
Natural Recovery of Sediments Predicted to Occur
Depth Interval:
Remedial Action Levels:
Depth Interval:
Remedial Action Levels:
Mud line
4 in
(10cm)*'
2ft
(60 cm).
Notfcr.
a)
b)
T
Sediment
COC
> 41 SQS
> 4 Human Health
(apply site-wide)
•12 mg/kg oc PCB'
•57 mg/kg dw Arsenic
•1,000 tig TEQ/kg dwcPAH
•25 ng TEQ/kg d w Dioxins/ Furans
Sediment S(^S
COC
> 4 Human Health
•12 mg/kg OC PCBC
•57 mg/kg dw Arsenic
*1,000 ^Lg TEQ/kg d w cPAH
•25 ng TEQ/kg dw Dioxins/ Furans
>
n
r+
<'
(D
XI
ft)
3
fD
Q.
Oi"
r+
o"
a*
Mud line
4 in
(10cm)
2ft
(60cm)
Sediment
*COC
J
> 39 SMS at 2x SQSd
Sediment
COC
> 4 Human Health
(apply site-wide)
•12 mg/kg OC PCB'
•57 mg/kg dw Arsenic
•1,000 ng TEQ/kg dw cPAH
•25 ng TEQ/kg dw Dioxins/ Furans
Potential Tug Scour
Elevations (128
acres)0
• RGBs at 3x CSL
•195 mg/kg OC PCBs
Deep Elevations (105
acres)e
• No RAL in 0-2ft interval
>
o
rHh
<'
fD
CD
3
fD
Q_
QJ°
ft
O*
13
COC =
SQS =
Risk Driver Contaminant of Concern
Washington Sediment Quality Standard
299subtidal acre* excludes 14 subtidal acres In Early Action Areas.
Active Remediation - dredge, cap, ENR, or a combination thereof. See remedial technology applications In flowcharts In Figures 18a andb
c) The dry weight equivalent of this RAL (240 pg/kg dw PCB assuming 294 organic carbon ) was used In the FS for mapping purposes.
d) RAl Is ,r2XSQS and not to exceed CSL" This RAL for surface sediments would only be used for 39 of the 41 SQS COCs, and would not be used foi any of the four human
cPAH, and dioxins/furans), If SQS Is not met 10 years after remedial action, contingency actions may be needed.
e) Potential tug scour elevations are shown in Figure 3 of the Supplemental Scenarios Memo. These are defined as -4 to -24 ft MLLW north of 1'* Ave S Bridge and -4 to -18 ft MLLW south of Vx Ave S Bridge.
Deep elevations are defined as deeper than -24 ft MLLW north of L" Ave S Bridge and deeper than -IS ft MLLW south of 1* Ave S Bridge.
COCs (PCBs, arsenic,
Figure 22. Subtidal Areas - Remedial Action Levels Application
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Proposed Plan — Lower Duwamish Waterway Superfund Site
11 Key Terms
Applicable or Relevant and Appropriate Requirements (ARARs) - under CERCLA Section 121,
remedial actions must comply with or EPA must formally waive any standard, requirement, criteria or
limitation under Federal environmental laws or more stringent State environmental or facility siting laws.
Bed Composition Model (BCM) - along with the Sediment Transport Model, this was a tool used in the
Feasibility Study to predict future contaminant concentrations in LDW sediments during and following
implementation of each of the proposed cleanup alternatives.
Benthic Invertebrates - sediment-dwelling organisms such as amphipods, clams, and oligochaete
worms.
CERCLA - the Comprehensive Environmental Response, Compensation, and Liability Act—also known
as Superfund—CERCLA is a Federal law which authorizes response actions to reduce the dangers
associated with releases or threats of releases of hazardous substances that may endanger public health or
the environment.
Contained Aquatic Disposal (CAD) - disposal of dredged sediment in a depression or bermed area at
the bottom of a water body. The area is then capped with clean sediment.
Contaminant of Concern (COC) - a hazardous substance or group of substances that pose unacceptable
risk to human health or the environment.
Enhanced Natural Recovery (ENR) - an active remedial technology which includes placement of a thin
clean sand or sediment layer as a means to accelerate recovery.
Excess Lifetime Cancer Risk - the incremental probability of an individual developing cancer over a
lifetime as a result of exposure to a carcinogen.
Food-Web Model (FWM) - a model that estimates the relationship among sediment, water, and tissue
contaminant concentrations.
Hazard Index (HI) - the sum of more than one hazard quotient for multiple substances and/or multiple
exposure pathways. The HI is calculated separately for chronic, subchronic, and shorter-duration
exposures. An HI may be used to evaluate the risk for multiple non-carcinogenic hazardous substances
with similar modes of toxic action.
Hazard Quotient (HQ) - a method to summarize the relative level of risk for a single non-carcinogenic
hazardous substance that is based on the ratio of an exposure over a specified time period to a reference
dose.
Human Health Risk assessment (HHRA) - an assessment to determine potential pathways by which
humans could be exposed to contamination at or from a site. The assessment determines the amount of
exposure, and estimates the resulting level of toxicity.
In situ Treatment - an active remedial technology conducted in place (e.g., without removing sediment).
It includes reactive caps and amendments that enhance breakdown of or bind contaminants.
Institutional controls (ICs) - non-engineered measures that may be selected as remedial or response
actions either by themselves or in combination with engineered remedies, such as administrative and legal
controls that minimize the potential for human exposure to contamination by limiting land or resource
use.
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Proposed Plan — Lower Duwamish Waterway Superfund Site
Lowest Observed Adverse Effect Level (LOAEL) - the lowest contaminant concentration documented
to have shown a related negative impact on the reference species either from observation or by
experiment.
Mean Lower Low Water (MLLW) - the average height of the lowest tide recorded at a tide station each
day over the period from 1983 to 2001.
Model Toxics Control Act (MTCA) - a Washington State hazardous substances law generally similar to
CERCLA. MTCA establishes substantive requirements for cleanup actions (as State ARARs) when those
requirements are more stringent than CERCLA requirements. MTCA includes the SMS and its numerical
and biological standards for the protection of marine benthic invertebrates.
Monitored Natural Recovery (MNR) - MNR is a passive remedial technology that relies on natural
processes to reduce ecological and human health risks to acceptable levels, while monitoring recovery
over time to verify remedy success.
Natural Background - as defined in MTCA regulations, the concentrations of hazardous substances that
are consistently present in an environment that have not been influenced by localized human activities.
For some contaminants such as PCBs, background conditions may be influenced by global-distribution
patterns.
Organic Carbon (OC) Normalized Values -the bioavailability and toxicity of some organic
contaminants in sediments have been found to correlate with the organic carbon content of sediment.
Therefore, some SMS criteria have been set on an OC-normalized basis. An OC-normalized sediment
value is determined by dividing the dry weight value by the fraction of total OC present in the sample.
Preliminary Remediation Goals (PRGs) - contaminant concentrations that are developed during an
RI/FS. They are based upon applicable or relevant and appropriate requirements (ARARs) and other
information whenever ARARs are not adequately protective of all receptors at a site, such as
concentrations associated with the 1 in 1,000,000 cancer risk or an HQ equal to 1 for non-carcinogens
calculated from EPA toxicity information.
Principal Threat Waste (PTW) - a source of hazardous substances that is highly toxic or highly mobile,
such as pools of non-aqueous phase liquids, and that generally cannot be reliably contained or would
present a significant risk to human health or the environment should exposure occur.
Reasonable Maximum Exposure (RME) - the risk assessment scenario which portrays the highest level
of human exposure that could reasonably be expected to occur.
Recovery Categories - categories used to assign remedial technologies to specific areas based on
information about the potential for sediment contaminant concentrations to be reduced through natural
recovery or for subsurface contamination to be exposed at the surface due to erosion or scour (Category 1
- recovery presumed to be limited, Category 2 - recovery less certain, and Category 3 - recovery
predicted to occur).
Remedial Action Levels (RALs) - contaminant-specific sediment concentrations designed to identify
specific areas of sediments that require active remediation, taking into consideration the human health and
ecological risk reduction achieved by the different remedial technologies.
Remedial Action Objectives (RAOs) - objectives that describe what the proposed cleanup is expected to
accomplish in order to protect human health and the environment.
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Risk-based Threshold Concentrations (RBTCs) - the calculated concentrations in any medium
estimated to be protective of a particular receptor for a given exposure pathway and target risk level.
RBTCs are based on the baseline risk assessments conducted during the RI. Consistent with the the NCP
and as required by MTCA for final Washington cleanups (WAC 173-340-700(5)(b), (6)(d); 705(2), (4)-
(6)), sediment PRGs were set at a RBTC of 1 in 1,000,000 lifetime excess cancer risk for individual
hazardous substances, or 1 in 100,000 for multiple hazardous substances cumulatively, and anoncancer
HQ of 1.
Sediment Transport Model (STM) - a three-dimensional model developed to simulate sediment
movement over a wide range of flow and tidal conditions to inform the type of sediment cleanup
technologies that would be appropriate for the LDW. See also Bed Composition Model.
Storm Drain (SD) - a collection, conveyance, and related discharge outfall location from public or
private storm water systems. Unless designated as combined sewer overflows (CSOs) storm drains are not
connected to sewer water systems.
Toxic Equivalent (TEQ) - a single value used to express the joint toxicity of a mixture of compounds
with a similar toxic action.
95% Upper Confidence Limit (UCL95) on the Mean - the UCL95 is used to estimate exposure to
human health, fish, and wildlife to concentrations of hazardous substances in the environment. It is
intended to ensure that these concentrations are not underestimated when a number of values are
averaged. Use of this statistic assures no more than a 5% chance that the average of point concentrations
will be exceeded.
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12 Key Documents
RI Report - Windward Environmental LLC 2010. Lower Duwamish Waterway Remedial Investigation,
Remedial Investigation Report. Final. Prepared for Lower Duwamish Waterway Group for submittal
to U.S. Environmental Protection Agency, Seattle, WA and Washington State Department of
Ecology, Bellevue, WA. July 2010.
FS Report - AECOM 2012a. Final Feasibility Study Lower Duwamish Waterway, Seattle, Washington.
For submittal to: The U.S. Environmental Protection Agency Region 10 Seattle, WA and The
Washington State Department of Ecology Northwest Regional Office, Bellevue, WA. October 2012.
FS Supplement - AECOM 2012b. Technical Memorandum: Supplement to the Feasibility Study for the
LDW Superfund Site, Approaches for Addressing Additional Concerns in Alternative 5C and
Development of ALT 5C Plus Scenarios. Prepared for Lower Duwamish Waterway Group for
submittal to U.S. Environmental Protection Agency, Seattle, WA and Washington State Department
of Ecology, Bellevue, WA. December 2012.
FS Supplement Technical Memorandum - AECOM 2013. Development of Final Technology
Assignments and Modifications to Alternative 5C Plus Scenario 5a in Support of EPA's Preferred
Alternative. . Prepared for Lower Duwamish Waterway Group for submittal to U.S. Environmental
Protection Agency, Seattle, WA and Washington State Department of Ecology, Bellevue, WA.
February 2013.
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