EPA Superfund Site

COMMENCEMENT BAY, SOUTH TACOMA CHANNEL

WA | EPA ID WAD980726301

About this site’s exposure pathways: As of April of 2024, the Well 12A, Operable Unit 1 of the Commencement Bay (CB)/South Tacoma Channel (STC) Superfund site is considered “Current Human Exposure Not Under Control” (HENC). The Well 12A operable unit of the CB/STC site has undergone various remedial actions since 1983 to address soil and groundwater contamination that posed unacceptable risk to the City of Tacoma municipal water supply. Contaminants at this site are tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dischloroethene (cis-1,2-DCE), trans-1,2-dichlorothene (trans,1,2-DCE), vinyl chloride, and 1,1,2,2-tetrachloroethane (1,1,2,2-PCA). The remedial efforts undertaken at the site have successfully addressed exposure risks from direct contact with soil and groundwater drawn from Well 12A.
To assess the exposure risk for building occupants within the CB/STC site footprint, EPA recently completed a vapor intrusion (VI) investigation that included more than fifteen businesses locations and occupied parcels of land. TCE was the COC most commonly encountered in soil gas and indoor air within the study area at concentrations above commercial vapor intrusion screening levels and risk-based screening levels (RSL). 1,1,2,2-PCA was the other site-attributable COC detected in indoor air above the RSL. TCE has been detected in indoor air at three locations (two businesses in a common retail property, and a third second floor space) within this study area at concentrations above the “not to be exceeded” (NTBE) screening level values established by EPA Region 10 human health risk assessors to be protective of fetal cardiac developmental abnormalities. The EPA considers these considers these exceedances unacceptable.
The EPA is planning for a Time Critical Removal Action (TCRA) to address those locations where TCE has been identified in indoor air at concentrations above the NTBE screening level. The TCRA will include the installation of a sub-slab depressurization system (SSDS) and deployment of air purifying units (APU) to mitigate the exposure risks. The SSDS will be installed beneath those businesses in the common retail space where the highest concentration of TCE have been detected in indoor air. The SSDS will capture and reroute soil gas before it can enter the overlying building. The APUs will be deployed at the second location where the route from soil gas to indoor air is less clear to remove TCE from indoor air.
Individual may minimize risks inherent at this site by limiting the time spent indoors in areas where TCE has been detected above the NTBE or RSL values. If you are a building occupant, your exposure risk may be reduced by keeping windows and doors open during occupancy, taking other similar measures to enhance the flow of fresh/outdoor air to this space, or by minimizing the use of vacuum inducing systems (such as kitchen exhaust fans) outside of business hours. EPA currently anticipates that human exposure will be under control by Spring of 2025 when the TCRA is expected to be complete.
EPA regularly communicated VI study findings to those property and businesses owners included in the VI study footprint and has begun logistical coordination with owners of the properties included in the TCRA. Upon completion of the TCRA, EPA will continue to study the Site to better understand the exact source of soil vapors, and what measures can be taken to address these vapors at their source.