WA DOT Signals Maintenance
3700 9th Ave S, Seattle, WA 98134

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A release of petroleum hydrocarbons to soil at the Site was reported to Ecology in 1991, when three 5,000-gallon capacity underground storage tanks (USTs) were upgraded. The laboratory analysis indicated that soil surrounding the USTs was contaminated with petroleum.


In 2015, the three USTs with the associated piping and refueling system were removed due to termination of the land usage as a refueling facility. Petroleum contamination in the diesel and oil range was detected above cleanup levels in the soil. None of the other chemicals or metals sampled for were detected above cleanup levels. Ecology completed a Site Hazard Assessment (SHA) in 2015. The resulting SHA rank for the Site was 5, based on a scale of 1 to 5, where 1 represents the greatest potential impact to human health and the environment.


The Washington State Department of Transportation conducted a cleanup action during the UST removal in 2015 that included:

• Excavation of the three USTs and disposal of 562 tons of contaminated soil at a permitted facility;
• Collection of five soil samples at the bottom and sidewalls of the excavation to confirm removal of all contaminated soil. The results from these samples indicated contaminated soil was removed; groundwater was not sampled during the tank removal activities.

An Ecology contractor performed a Supplemental Site Investigation in 2017 to further evaluate the status of the contamination in soil and to assess if groundwater had been impacted. The activities included the installation of ten soil borings for soil and groundwater sampling within the former UST excavation and vicinity. The laboratory results for soil and groundwater did not exceed state cleanup standards. The Supplemental Site Investigation confirmed that the concentrations of petroleum contaminants at the Site do not pose a threat to human health and the environment.


Map showing site location as King County, WA SITE INFORMATION


View Electronic Documents

Cleanup Site Details Report

Facility Site ID: # 60549963

Cleanup Site ID: 9862

Seattle, King County

Status: Cleanup Started   Get definitions of Status terminology

Sunny Becker
Chinese Translator
(425) 649-7187

Tamara Cardona
Site Manager
(425) 649-7136

Nancy Lui
Public Involvement Coordinator
(425) 649-7117

Document Repositories:

Northwest Regional Office
3190 160th Ave SE
Bellevue, 98008-5452

Seattle Public Library - Beacon Hill Branch
2821 Beacon Ave S
Seattle, 98144