Block 38 West

This Site was issued a No Further Action Letter on March 25, 2026.

This site has been cleaned up and complies with the standards in the state’s environmental cleanup law, the Model Toxics Control Act. See the Site Details report at left or the documents below to learn more about this site. Ecology works to clean up contaminated properties throughout the state. Cleanups are construction projects that remove, treat, or contain potentially harmful substances.

Site Location

The Block 38 West Site is located in the South Lake Union neighborhood of Seattle. The Site includes the Block 38 West Property, a portion of the Westlake Avenue North right of way, and a north-south-trending alley (City of Seattle public right-of-way) east of the Block 38 West Property.

Site Background

Historical operations and placement of contaminated fill at the Block 38 West Property resulted in contaminated soil and groundwater at the Site.

From October 2019 through July 2021, substantial cleanup of the Block 38 West Site was performed through interim actions (early partial cleanups) on the Block 38 West Property and east-adjacent alley. These interim actions included removal and disposal of contaminated soil and were implemented in conjunction with the redevelopment of the Block 38 West Property.

Redevelopment

Redevelopment of the Block 38 West Property began in late October 2019. The former structures were demolished and a multi-story mixed-use building with 12 stories above street level and 4 levels of underground parking was constructed. Construction of the new building required mass excavation across the entire Block 38 West Property to approximately 30 to 35 feet below ground level.

Contaminants of Concern

Between 1994 and 2024 multiple phases of the Remedial Investigation were executed to assess the Site for contaminants of concern and to establish cleanup levels. Investigations found the following contaminants in soil and/or groundwater:

• Petroleum hydrocarbons as diesel-range organics (DRO), oil-range organics (ORO), and gasoline-range organics (GRO)
• Benzene
• Naphthalenes, including 1-methylnaphthalene and 2-methylnaphthalene
• Carcinogenic polycyclic aromatic hydrocarbons (cPAHs), including benzo(a)pyrene
• Metals (barium and mercury)

These contaminants were present at levels that exceeded standards under the state’s cleanup law, the Model Toxics Control Act (MTCA). Most of the contamination was removed during the interim actions. The interim actions constitute a permanent cleanup action to the maximum extent practicable in accordance with MTCA and current and future land use.

Remaining Contamination

A small amount of contamination remains in shallow soil in areas adjacent to the new building. The remaining contaminants in soil include total DRO+ORO and cPAHs. Those areas were not accessible for complete removal of the contamination during the interim actions due to the presence of underground utilities and structural elements. The areas of remaining contamination are contained through the use of engineered controls called a cap, which consists of asphalt or concrete pavement.

Institutional controls per the requirement of an Environmental Covenant are in place to prohibit or limit activities that may interfere with the integrity of the engineered controls (protective cap) or result in exposure to contamination. The remedy also includes required operation and maintenance of the protective cap with annual inspections.

The Model Toxics Control Act (MTCA) 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 MTCA and oversees cleanups. The MTCA site cleanup process is completed in steps over a variable timeline.