Commencement Bay Nearshore/
Tideflats Superfund Site
Asarco Sediments/Groundwater
Operable Unit 06
Ruston and Tacoma, Washington
Record of Decision
July 2000
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PARTI
Site Name and Location
Commencement Bay Nearshore/Tideflats (CB/NT) Superfund Site
Asarco Sediments/Groundwater Operable Unit 06
Tacoma and Ruston, Washington
U.S. Environmental Protection Agency (EPA) ID No. WAD980726368
Statement of Basis and Purpose
This decision document presents the Selected Remedy for Asarco Sediments/Groundwater
Operable Unit 06 (OU 06) in Tacoma and Ruston, Washington. The Selected Remedy was
chosen in accordance with Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and
Reauthorization Act of 1986 (SARA), and, to the extent practicable, the National
Contingency Plan (NCP). This decision is based on the Administrative Record for this Site.
The State of Washington Department of Ecology (Ecology) concurs with the Selected
Remedy.
Assessment of the Site
The response action selected in this Record of Decision (ROD) is necessary to protect public
health, welfare, or the environment from actual or threatened releases of hazardous
substances into the environment. Such a release or threat of release may present an
imminent and substantial endangerment to public health, welfare, or the environment.
Description of the Selected Remedy
The Asarco Sediment/Groundwater Operable Unit (OU 06) Site ("Site") is one of the
operable units that specifically addresses contamination coming from, or related to, the
Asarco Smelter Facility ("Facility") in Ruston and Tacoma, Washington. The Selected
Remedy for the Asarco Sediments/Groundwater Operable Unit 06 includes the following
elements:
Groundwater
Groundwater at the Asarco Facility was originally studied in an RI/FS concluded in 1993
(Hydrometrics, August 1993). The Asarco Tacoma Smelter ROD (OU 02 ROD) identified the
selected remedy for onsite waste materials, contaminated soil, and surface water (EPA,
1995). However, the OU 02 ROD deferred a remedy decision for groundwater and called for
further monitoring. This ROD for OU 06 identifies the Selected Remedy for groundwater.
Although the Selected Remedy for groundwater was not addressed by the OU 02 ROD, a
number of elements in the OU 02 remedy will directly benefit groundwater quality. These
elements include capture of shallow groundwater in selected areas, construction of a low-
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PARTI
permeability cap across the Facility, and excavation of the most highly contaminated source
materials (selected slag material and contaminated soils) and consolidation of these
materials into an On-site Contaminant Facility. These OU 02 remedy elements will
(1) remove a significant source of contamination that would otherwise impact groundwater
quality and (2) significantly reduce the flow of contaminated groundwater to
Commencement Bay by minimizing recharge of the shallow aquifer system (e.g., surface
water controls and the low-permeability cap will reduce infiltration).
EPA has determined that additional remedial actions, over and above those already being
implemented under OU 02, are not necessary to address groundwater under this ROD for
OU 06. As a result this ROD summarizes the elements of the remedy for OU 02 that will
benefit groundwater and identifies other elements of the groundwater remedy not
previously addressed. These other remedy elements include finalization of the groundwater
remedial action objectives (RAOs), identification of cleanup levels and groundwater point of
compliance, and long-term monitoring requirements.
Specifically, the Selected Remedy for groundwater, as represented by the RODs for OU 02
and OU 06, includes the following elements:
Reduce groundwater flow and related contaminant loading to Commencement Bay by
removing the most significant source materials and limiting groundwater recharge to
aquifers beneath the smelter portion of the Facility. Groundwater control will be
achieved by intercepting groundwater with subsurface drains in selected locations,
diverting surface water and installing a low-permeability cap over the smelter portion of
the Facility. These controls will minimize infiltration and recharge of onsite aquifers.
(These remedy elements are being accomplished under OU 02 cleanup.)
Continue to monitor groundwater to evaluate the long-term effects that the Facility
cleanup will have on future groundwater quality. (Addressed for the first time in this
ROD for OU 06.)
Implement institutional controls to restrict future use of Facility groundwater.
(Addressed for the first time in this ROD for OU 06.)
Sediment
The Selected Remedy for marine sediments includes the following elements:
Dredge contaminated sediment in the Yacht Basin and place the dredged sediment
beneath a low-permeability soil cap to be constructed on the upland portion of the
Facility (i.e., OU 02). The sediments will be contained under the low-permeability cap at
an elevation such that groundwater will not come in contact with the sediment.
Monitor the dredged area in the Yacht Basin to verify that it does not become
recontaminated.
Cap contaminated sediments in selected offshore areas.
Monitor the sediment caps to confirm that they remain in place, continue to isolate the
underlying contaminated sediment, become recolonized with healthy biological
communities, and do not become recontaminated.
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Use institutional controls to prevent activities that could damage the sediment caps.
Monitor the areas outside the capped and dredged areas to confirm that these areas
meet RAOs.
The Selected Remedy for the Asarco Sediments/Groundwater OU 06 has been chosen to
complement the remedy previously selected for OU 02 (EPA, March 1995). The OU 02
remedy is currently being implemented.
Statutory Determinations
The Selected Remedy is protective of human health and the environment, complies with
federal and state requirements that are applicable or relevant and appropriate to the
remedial action, is cost-effective, and utilizes permanent solutions and alternative treatment
technologies to the maximum extent practicable with the following exceptions. The federal
National Toxics Rule (NTR) standard for arsenic of 0.14 (J.g/L (40 CFR Section 131.36) is a
relevant and appropriate requirement for groundwater but is being waived for reasons
discussed in Part II of this ROD (Section 12.1.1 of the Decision Summary).
The Selected Remedy for OU 06 does not satisfy the statutory preference for treatment as a
principal element of the remedy for the following reasons:
Groundwater. Groundwater treatment is not viable or cost-effective because source
materials remain on the Site. Further, a pump and treat remedy for containment
purposes would be inefficient due to the direct hydraulic connection that the Site
aquifers have with the waters of Commencement Bay. Treatment would require
groundwater extraction in perpetuity at very high pumping rates. The most significant
source of groundwater contamination is the slag material that is present below the water
table throughout most of the Facility. This source material will continue to leach
contaminants to groundwater. The Selected Remedy focuses on restricting recharge to,
and flow through, the affected water-bearing zones such that the volume of
groundwater discharged to Commencement Bay is reduced to the maximum extent
practicable.
Sediments. Treatment technologies were evaluated for possible application to sediment
cleanup, but were not carried forward because: (1) there are currently no effective and
appropriate in situ treatment technologies (i.e., treating in place) for sediments similar to
those at the Site, and (2) any ex situ treatment would require significant material
handling (e.g., dredging, de-watering, transporting, processing) and treatment
processing at extreme cost (e.g., construction costs could be as high as $75 million to
$100 million), with little or no additional benefit to the effectiveness of the remedy.
Because the Selected Remedy will result in hazardous substances, pollutants, or
contaminants remaining onsite above levels that allow for unlimited use and unrestricted
exposure, a review will be conducted within five years after initiation of remedial action to
ensure that the remedy is, or will be, protective of human health and the environment.
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Data Certification Checklist
The following information is included in the Decision Summary of this ROD (Part 2).
Additional information can be found in the Administrative Record for this Site.
Chemicals of concern and their respective concentrations Sections 5 and 7.
Baseline risk represented by the chemicals of concern Section 7.
Cleanup levels established for chemicals of concern and the basis for these levels
Section 12.
How source materials constituting principal threats are addressed Section 11.
Current and reasonably anticipated future land use assumptions and current and
potential future beneficial uses of groundwater used in the baseline risk assessment and
ROD Sections 6 and 7.
Potential land and groundwater use that will be available at the Facility as a result of the
Selected RemedySection 6.
Estimated capital, annual operation and maintenance (O&M), and total present worth
costs, and the number of years over which the remedy cost estimates are projected
Sections 9 and 12.
Key factors that led to selecting the remedy Section 12.
Authorizing Signature
Chuck Findley Date
Acting Regional Administrator
[Original signed by Chuck Findley on July 14,2000]
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