We invite you to review and comment on the periodic review for the Kent Highlands Landfill site, located in King County.
The Kent Highlands Landfill site is located at 23076 Military Road South in Kent, Washington.
The Seattle Solid Waste Utility started landfilling operations in 1968. The landfill received mostly municipal garbage until 1983. After 1983, the landfill also took in industrial wastes and construction debris. Disposal operations terminated in 1986. The landfill is adjacent to the Green River. An environmental covenant restricts activities that might result in exposures to the contaminants.
A periodic review is conducted every five years following a cleanup when some contamination remains. The purpose of the review is to evaluate site conditions and ensure continued protection of human health and the environment.
The 2019 periodic review focuses on three areas: (1) activities undertaken by the City of Seattle in response to the previous periodic review, (2) actions that need to be performed or modifications that need to be considered during the next five year period, and (3) a protectiveness discussion.
The remedy required by the Cleanup Action Plan at the landfill remains protective of human health and the environment with respect to refuse encapsulation, landfill gas control, stormwater quality maintenance, and leachate capture. Vinyl chloride continues to exceed regulatory values in groundwater, which discharges to surface water (the Green River).
There is no current use of the river for drinking water adjoining the landfill and vinyl chloride dissipates quickly in surface water. Therefore, the landfill failed the periodic review because of regulatory value exceedances, but additional information is necessary to determine if further remedial action is necessary.
Ecology and the City of Seattle are continuing to monitor and manage the landfill and are discussing the next steps to address the exceedances.