The Pasco Sanitary Landfill covers 250 acres near Pasco, Washington. It operated as an open burning dump from 1958 to 1971 and then as a sanitary landfill starting in 1972. Between 1972 and 1975, part of the site accepted hazardous wastes, including thousands of drums of paints, resins, herbicide and pesticide manufacturing wastes, and caustic chemicals. Those operations contaminated groundwater beneath and downgradient of the property with volatile organic compounds (VOCs), which are carbon-based chemicals that evaporate easily. The site was added to the National Priorities List (NPL), the federal Superfund program's roster of priority cleanup sites, on February 21, 1990. The Washington State Department of Ecology is the lead cleanup agency.
A final remedy was selected on August 21, 2019, and cleanup construction began in October 2020. From 2021 onward, contractors excavated and removed more than 35,000 drums of hazardous waste and debris from Zone A for off-site disposal. Between April 2024 and May 2025, crews ran an in-situ thermal remediation (ISTR) system in Zone A. ISTR heats contaminated soil to about 250 degrees Fahrenheit using buried heating rods spaced 12 feet apart. Steam and contaminants are drawn to a treatment system where heavy materials are condensed and stored, and remaining vapors are destroyed in a thermal oxidizer to meet air quality standards.
In early November 2024, some chemicals from the thermal treatment process were not fully captured and traveled to groundwater. Groundwater in the area is not used for drinking water, and people are not currently at risk. Ecology installed soil gas samplers to check for vapor intrusion, the process by which contaminants can move from soil or groundwater into indoor air. Testing in early December 2024 showed groundwater does not pose a risk to air quality inside nearby buildings. A new groundwater treatment system is being designed to prevent contamination from spreading off-site, with monitoring occurring every three weeks. Final cover construction over Zone A is scheduled for June 2025 and beyond.
EPA has determined that human exposure is under control across the entire site and that contaminated groundwater migration has been stabilized with no unacceptable discharge to surface water. Physical construction of the cleanup is not yet complete. Two businesses currently operate on the site, employing 44 people and generating about $10.9 million in annual sales.
Community members with questions can contact the EPA Remedial Project Manager or the EPA Community Involvement Coordinator for the site.
