Seattle DOT Dexter Parcel
615 Dexter Ave N, Seattle, WA 98109

Aerial view of Seattle DOT Dexter Parcel site
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This Site is part of a multi-property transaction associated with the Mercer Mega-Block Development project in Seattle’s South Lake Union neighborhood. The Seattle DOT Dexter Parcel Site is also part of the property transaction and development project. Please see the web page for Seattle DOT Mercer Parcels for details and documents related to that site. 




Información en español

Información del Sitio 
 Someta sus

Reunión pública en


Ecology is hosting a public comment period from December 6, 2021 – January 19, 2022 to get input on the following cleanup documents for the Seattle DOT Dexter Parcel Site:

Prospective Purchaser Consent Decree (PPCD) – legal agreement that directs the Prospective Purchaser to implement cleanup of the Site in accordance with the Cleanup Action Plan (below) once it has completed its purchase.  

Remedial Investigation (RI) – describes contamination at the Site. To view the RI appendices, please click 'View Electronic Documents' link to right. 

Feasibility Study (FS) – evaluates and recommends a permanent cleanup action as the preferred alternative.

Draft Cleanup Action Plan (dCAP) – describes Ecology’s chosen cleanup plan and specifies cleanup standards and requirements for the Site.

State Environmental Policy Act – Determination of Non-Significance (SEPA) – evaluation and determination that the proposed cleanup at the Site is not likely to cause harm.

State Environmental Policy Act - checklist

Public Participation Plan (PPP) –  describes how Ecology will engage with the community and keep the public informed.

Submit your comments

View our Factsheet (English)

Online public meeting

On January 6, 2022, Ecology held an online public meeting to present on the cleanup projects.  You can view the slides for this presentation here:

Public presentation slides

Current view of Site looking west from Dexter Ave N.
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The Seattle DOT Dexter Parcel Site is generally located at 615 Dexter Avenue North (Property) in the South Lake Union neighborhood of Seattle.  The Property is 0.56 acres and bounded to the north by Roy St, to the south by an alley, to the east by Dexter Ave N, and to the west by Aurora Ave North. Contamination at the Site is present on a portion of the Property and extends into an adjacent alley.

Site History

Private residences existed on the Property until the early 20th century.  In the 1920s, a building was constructed on the southern portion of the Property, and later expanded to the north and east in the 1940s. Various commercial and light industrial businesses occupied the building, including sandpaper, hardwood flooring and woodworking companies, a coated wall board manufacturer, a plastic mixing and storage facility, and a restaurant.  Most
recently, a copier sales and service business occupied the building.  A fueling and service station also operated on the Property during the 1930s and 1940s. 

In 2005, a fire destroyed a portion of the main building.  A parking lot replaced the damaged structure. 

Image of proposed redevelopment. Credit: Alexandria Real Estate Equities, Inc.
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The Property is planned to be redeveloped with an 18-story tower and a below-grade parking garage that will encompass the entire footprint of the Property. Two levels of below-grade parking are planned. The building will be a multi-family residential tower and will include a mix of units including market rate and income-restricted units ranging from 60 to 85 percent Area Median Income. Redevelopment is expected to begin in 2023 and is expected to be completed by 2024.


Investigations at the Site found the following contaminants in soil and/or groundwater:

•Gasoline-range petroleum hydrocarbons

•Diesel-range petroleum hydrocarbons


These contaminants are present at levels that exceed allowable standards under the state’s cleanup law, the Model Toxics Control Act (MTCA), and will be addressed during the Cleanup Action.


The FS developed three cleanup alternatives that were evaluated for the Site based on permanence, effectiveness, protectiveness, implementability, short- and long-term risk, public concerns, and cost. From that evaluation, a preferred alternative was identified and developed into a draft CAP. The preferred alternative consists of the following actions to clean up the contaminated areas of the Site:

•Excavating contaminated soil and groundwater within the redevelopment excavation area on the Property and transporting it off-site for treatment and/or disposal.

•Injecting oxygen-release compound (ORC®) into the contaminated area within the adjacent alley to enhance in situ bioremediation processes.

•Implementing monitored natural attenuation for remaining contamination in the alley and for any residual contaminated groundwater that may remain on the Property below the planned redevelopment excavation.

•Installing a vapor barrier to protect occupants of the new building from exposures to remaining contamination until concentrations decrease to protective levels.

•Maintaining a protective cap over remaining contamination at the Site.

•Implementing institutional controls to maintain protective barriers and place restrictions on land use to prevent exposures to remaining contamination until concentrations decrease to protective levels.

•Performing compliance monitoring and maintenance.

The draft CAP also includes contingency actions that would be implemented if additional contamination is discovered beneath the existing building following its removal, and to facilitate more rapid remediation of contaminated groundwater in the alley if monitored trends indicate that full compliance would not be met within the estimated restoration time frame. Implementation of this cleanup action will address the cleanup action objectives for the Site.

Site map. Petroleum hydrocarbons in soil is in solid red and in groundwater in red lines. Planned excavation area is within the dashed purple lines. Monitored natural attenuation is in blue. Planned treatment injection locations are in yellow and black
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The Seattle DOT Mercer Parcels is part of the South Lake Union neighborhood, which is located next to downtown Seattle and bordered on the north by Lake Union. This area has a long history of industrial and commercial activities which caused contamination of the soil and groundwater. Currently, this area is undergoing extensive redevelopment as new buildings are constructed for commercial and residential use. Ecology is working with property owners to clean up contamination present at the Site and other nearby sites to reduce impacts to human health and the environment. 


The Model Toxics Control Act (MTCA; Chapter 70.105D RCW is Washington’s environmental cleanup law). It provides requirements for contaminated site cleanup and sets standards that protect human health and the environment. Ecology enacts the MTCA and oversees cleanups. The MTCA site cleanup process is completed in steps (see graphic below) over a variable timeline.

Please click on the photo for a larger view


Map showing site location as King County, WA SITE INFORMATION


View Electronic Documents

Cleanup Site Details Report

Facility Site ID: # 81735

Cleanup Site ID: 14785

Seattle, King County

Status: Cleanup Started   Get definitions of Status terminology

Tena Seeds
Site Manager
(425) 457-3143

Document Repositories:

Northwest Regional Office
15700 Dayton Ave N
Shoreline, 98133