The Koppers Company Oroville Plant operated as a wood-treating facility starting in 1948. Workers used pentachlorophenol, creosote, and arsenic-based compounds to treat railroad ties and telephone poles. Chemical fires and wastewater operations spread contamination into both soil and groundwater on and off the property. EPA added the site to the National Priorities List on September 21, 1984.
Contaminants of concern are found in soil and groundwater across the entire site. Metals include arsenic, barium, chromium, copper, and nickel. Organic compounds include benzene, toluene, ethylbenzene, and xylene. The site also contains polycyclic aromatic hydrocarbons (PAHs), carcinogenic PAHs, naphthalene, pentachlorophenol, dioxins, dibenzofurans, dichloromethane, and boron oxide.
EPA issued a cleanup decision in 1989 and amended it in 1996 and 1999. All contaminated soil was moved into an engineered on-site landfill with a lined and capped cover. For groundwater, the plan calls for extraction and treatment of the contaminated plume, an alternative water supply for affected residents, and deed restrictions limiting the property to industrial and commercial use. A portion of the groundwater plume was too densely contaminated to fully restore, so that zone is contained and monitored rather than remediated to drinking water standards. Physical construction of the cleanup finished on September 4, 2003.
Currently, the landfill shows no containment problems, and perimeter monitoring wells show no contaminants above cleanup standards. Three on-site extraction wells each pump about 150 gallons per minute and are making progress toward cleanup goals. Off-property groundwater has been restored to drinking water quality, and monitoring there ended in June 2013. All exposure pathways that could pose unacceptable risk are under control. The site achieved sitewide ready-for-anticipated-reuse status on June 26, 2006, and operation and maintenance activities continue. The most recent five-year review was completed on September 19, 2023, with the next review estimated between September and November 2028.
Community members with questions can contact the EPA's Community Involvement Coordinator or the Remedial Project Manager.
