King County Brownfields Program Executive Summary for MMCP

King County’s Solid Waste Division (SWD) provides garbage transfer and disposal, and recycling services for residents and businesses in King County, except for the cities of Seattle and Milton. SWD activities in the LDW drainage basin in 2017 involved the work of the King County Brownfields Program. The Brownfields Program is no longer in operation, but in past years it provided technical and financial assistance to qualified private individuals and businesses, nonprofit organizations, and municipalities in King County to assess and clean up contaminated sites, called brownfields. The program was funded, in part, with grants from the U.S. Environmental Protection Agency (EPA) to conduct environmental site assessments (ESAs) on properties with confirmed or suspected contamination. Over the last 19 years, the program conducted 12 Phase I and 27 Phase II ESAs, many of which have resulted in successful cleanup and redevelopment projects, including the development of affordable housing. Between 2008 and 2017, one project in the LDW drainage basin received extensive assistance from the Brownfields Program and EPA. The site, located in the Georgetown neighborhood of the City of Seattle, was formerly a gas station. Seattle-based artist collective SuttonBeresCuller (SBC) formed a 501(c)(3) nonprofit and purchased the property in 2013 to transform it into a pocket park and arts-oriented community center called the Mini-Mart City Park. Past assistance provided to the site includes the following.

1) A 2008 Phase I ESA that identified recognized environmental conditions (RECs), including: a former service station operation at the site that represented a potential source of petroleum contamination to soil and groundwater; pesticide residues that may have migrated through groundwater to the property from current and historical commercial nurseries located 500 feet northeast of the site; and petroleum hydrocarbons (TPH-G and BETX) detected in groundwater from former underground storage tanks (USTs) located at the King County International Airport maintenance shop located hydraulically upgradient from the site.

2) A 2009 geophysical investigation that identified as many as five potential UST sites and confirmed gasoline and diesel range petroleum hydrocarbons in soil and groundwater at concentrations that exceeded Ecology Model Toxics Control Act (MTCA) Method A cleanup levels. The investigation did not find significant impacts from solvents or pesticides.

3) A 2010-11 EPA Targeted Brownfields Assessment (TBA) conducted by EPA contractor EIGov that conducted additional sampling to further characterize the site. The TBA detected a contaminated groundwater plume trending southwesterly off the site.

4) A 2017 Supplemental Phase II ESA that obtained additional groundwater data upgradient and downgradient of the site that better defined the extent of petroleum‐related groundwater contamination. This investigation determined that the petroleum contaminated groundwater was not extensive and would be amenable to remediation by installation of a vapor barrier and mitigation/treatment system at the appropriate stage of construction. As of May, 2018, former building structures and underground tanks had been removed from the site, and SBC has been working with environmental consultant G-Logics to develop and install a combination air sparge and soil-vapor extraction system to address the petroleum contamination below the property. The system will be incorporated into the first phase of construction, and is
designed to initiate remediation of residual petroleum contaminants on the property and tomitigate vapor intrusion into the site buildings. SBC plans a groundbreaking ceremony for the Mini-Mart City Park in mid-2018. More information about the Mini-Mart City Park is available at https://www.minimartcitypark.com/. More information about the past work of the King County Brownfields Program is available at https://kingcounty.gov/depts/dnrp/solid- waste/programs/brownfields.aspx.