Block 38 West
520 Westlake Ave N, Seattle, WA 98109

Block 38 West - aerial view of Alley Interim Action Area.
Please click on the photo for a larger view


Updated December 2020

Ecology and City Investors IX L.L.C., the Potentially Liable Person (PLP), will conduct an interim cleanup (Interim Action) for the Block 38 West site (Site) under an Agreed Order with Ecology. The action will excavate contaminated soil on a portion of the Site.

Ecology is hosting a public comment period from December 21, 2020 - January 19, 2021 to get input on the following document:

Interim Action Work Plan – Alley Area of Block 38 West Site  – describes how the PLP will conduct a cleanup of contaminated soil in the alley, which includes the eastern portion of the Site.

Submit comments here

Factsheets for this public comment period are available:
Block 38 West Fact sheet -- English
Block 38 West Fact sheet - Español
Block 38 West Fact sheet - 訊息中文版

Why this cleanup matters

The Block 38 West Site 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

Currently, this area is undergoing extensive redevelopment as new buildings are constructed for commercial and residential use. Proposed construction activities at the Site could impact an existing groundwater contaminant plume located nearby.  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. 

Block 38 West Site - street view
Please click on the photo for a larger view


Site Location

The Block 38 West Site is located in the South Lake Union neighborhood of Seattle (see figure on page 2). The property known as Block 38 West is generally located at 500-536 Westlake Avenue North, is approximately 1.06 acres in size, and consists of three parcels (Property). 

Site History

Past uses of the Property include a lumber storage yard, a blacksmith shop, warehouse storage, and retail and commercial operations and associated parking.The Property’s structures have been demolished as part of plannedredevelopment of the Property.  The redevelopment includes construction of a multistory mixed-use building with a preliminary design for a 12-story office building above street level and four levels of parking below street level.

An independent cleanup action (without Ecology oversight) is currently ongoing at the Site in connection with redevelopment.


Previous investigations at the Site found the following in soil
and/or groundwater:
•  petroleum hydrocarbons (as diesel-range and oil-range organics)
•  polycyclic aromatic hydrocarbons (PAHs), including naphthalenes and
    carcinogenic PAHs (cPAHs)
•  benzene

 These contaminants were found at levels that exceed allowable standards under the state’s cleanup law, the Model Toxics Control Act (MTCA Chapter 70.015D RCW), and therefore must be addressed during the cleanup action. Cis-1,2-dichloroethene was also found in the groundwater but at concentrations below applicable cleanup levels under MTCA.


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: # 62773

Cleanup Site ID: 15008

Seattle, King County

Status: Cleanup Started   Get definitions of Status terminology

Tena Seeds
Site Manager
(425) 649-7008

Kelsey Ketcheson
Public Involvement Coordinator
(425) 649-7287