Commencement Bay, WA

A.8 Commencement Bay, WA

A.8.1 Contact

Regulatory Contact: USEPA

A.8.2 Summary

Environment:	Marine embayment
Scale:	Full
Contaminants of Concern:	Metals (arsenic, lead, zinc, cadmium, copper, mercury), PCBs, PAHs, volatile organic compounds (VOCs), and phthalates
Source Control Achieved Prior to Remedy Selection?	No
Final Remedy:	MNR (60 acres), cappingTechnology which covers contaminated sediment with material to isolate the contaminants from the surrounding environment. and dredging (240 acres)
Expected Recovery Time:	10 years

A.8.3 Site Description

The Commencement Bay Nearshore/Tideflats site is located in the southern end of the main basin of Puget Sound in the City of Tacoma and the Town of Ruston, Washington. There is an active commercial seaport on site that includes 10-12 square miles of shallow water, shoreline, and adjacent land. The majority of the area is highly developed and industrialized. Primary sources of contamination at this site include past and present wastewater discharges from numerous and varied industrial operations, as well as past and present nonpoint contributions to the watershed.

Various industrial activities have been operating in the vicinity since the turn of the century including shipbuilding, oil refining, chemical manufacturing and storage, and pulp and paper mills. Currently 281 industrial facilities are active in the site. 34 of these have NPDES permits for storm drain, seep, and open-water discharges; groundwater seepage; atmospheric deposition; and spills. In addition, the Tacoma-Pierce County Health Department identified several hundred nonpoint sources that discharge to Commencement Bay as well as 70 facilities that are ongoing contaminant sources. This site was added to the National Priorities List in 1983.

CSM summary: Primary natural recovery processes at this site include physical isolation, chemical transformationabiotic or biotic chemical process (such as photolysis, hydrolysis, oxidation/reduction, radioactive decay) that transform an element (Cr(VI) - Cr III) or compound (phenol – CO₂+ H₂O) to a different element or chemical compound. and dispersion1) Pollutant or concentration mixing due to turbulent physical processes; 2) A distribution of finely divided particles in a medium.. Lines of evidence collected to support these natural recovery processes include sediment traps to determine source controls and sediment inputs, sediment core profiling and radioisotope analyses to determine key fate and transport processes as well as document historical recovery rates. Models were then used to interpret this data and estimate sediment concentrations over a 10 year period.

A.8.4 Remedial Objectives

The primary concern for this case study is human health and ecological risk from PCBs, PAHs, 4-methylphenol, and VOCs.

The RAO/project objective for this site is “to achieve acceptable sediment quality in a reasonable time frame.” “Acceptable sediment quality” is defined as “the absence of acute or chronic adverse effects on biological resources or significant human health risks.” A “reasonable time frame” is defined as within 10 years following the completion of dredging and/or capping operations.

A.8.5 Remedial Approach

Final selected remedy: MNR (60 acres); capping and dredging (240 acres)

MNR was selected for several sites in the Commencement Bay Nearshore/Tideflats area including Hylebos Waterway, Area B of Sitcum Waterway, Middle Waterway, Thea Foss and Wheeler-Osgood Waterways. In addition, MNR would be accelerated if more contaminated sediments in the area were removed. The various components of these remedies include:

evaluation and control of upland sources of contamination
removal of sediments with chemical concentrations high enough to be internal sources of recontamination
capping areas of high concern for adverse biological effects or potential contamination from resuspensionA renewed suspension of insoluble particles after they have been precipitated. and bioaccumulationThe accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost. Thus, the longer the biological half-life of the substance the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high.
MNR or EMNR with thin-layer caps in areas of moderate concern
institutional controlsNon-engineered instruments, such as administrative and legal controls, that help minimize the potential for human exposure to contamination and/or protect the integrity of the remedy. (such as limits on fish or shellfish consumption and anchorage restrictions).

Primary lines of evidencePieces of evidence are organized to show relationships among multiple hypotheses or complex interactions among agent, events, or processes. A weight of evidence approach includes the assignment of a numeric weight to each line of evidence. used to investigate MNR: Modeling was used to support determinations of physical isolation, chemical transformation and dispersion. The models took into account additional mass deposition from ongoing sources, sediment deposition, and bioturbation.The displacement and mixing of sediment particles and solutes by fauna (animals) or flora (plants).

A.8.6 Monitoring

Monitoring elements: Monitoring activities aim to assess the performance of natural recovery processes and RAO attainment. Lines of evidence to support physical isolation include sediment coring and vertical profiling, radioisotope analysis, and sediment age dating and surface sediment chemistry and grain size analysis. Lines of evidence that support chemical transformation include PAH fingerprint analysis to assess vertical/lateral profiles and trends in chemical transformation. Lines of evidence collected to support risk reduction include the visual inspection of exposed tideflats to document benthic burrowing activity and biota tissue analysis.

Expected recovery time: 10 years

Projected monitoring costs: $310,000

RAOs/project objectives achieved? Overall MNR is viewed as a success where sufficient monitoring data have been collected (Sitcum Waterway). For Area B of the Sitcum Waterway, cleanup levels have been achieved with natural recovery. The long-term monitoring was deemed complete in 2004. Baseline monitoring has been completed and long-term monitoring is planned to begin in 2008 for the Theo Foss and Wheeler-Osgood Waterways.

A.8.7 References

USEPA Region 10, the Pacific Northwest: Commencement Bay-Nearshore Tideflats. http://yosemite.epa.gov/r10/cleanup.nsf/sites/cbnt.

Publication Date: August 2014

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