Iron Mountain Mine covers 4,400 acres in the Klamath Mountains, nine miles northwest of Redding, California. The site was mined periodically from the 1860s to 1963 for copper, iron, gold, silver, zinc, and other metals. Mining exposed ore and waste rock to oxygen and water, generating acidic drainage loaded with metals that seeped into local streams and the Sacramento River. That river supplies drinking water to Redding and other communities and supports threatened and endangered species including Sacramento River winter-run Chinook Salmon and Steelhead Trout. EPA added the site to the Superfund National Priorities List in 1983.
Contaminants identified at the site include aluminum, antimony, arsenic, cadmium, copper, iron, lead, mercury, nickel, silver, thallium, and zinc. These metals show up in leachate, solid waste, surface water, and sediment across multiple areas of the site. Cadmium, copper, and zinc are the metals found in surface water. Sediment contains arsenic, copper, iron, nickel, and zinc. The primary environmental risk is to aquatic life in the Sacramento River and downstream waterways.
The site is divided into six operable units. Five have Records of Decision covering water management, source control, an old mine seep, the Slickrock Creek area, and sediments. The sixth unit, the Boulder Creek area source, is still in the investigation stage. Cleanup began in 1988. Key actions include capping exposed mine wastes, diverting clean stream water away from contaminated zones, and treating acidic drainage. The Minnesota Flats Treatment Plant has operated since 1994, using a lime-based process to neutralize contaminated water at up to 9 million gallons per day. Since 2001, the cleanup has treated more than 9 billion gallons of acidic drainage and removed more than 14 million pounds of zinc, copper, and cadmium. No site-related water quality violations in the Sacramento River immediately downstream have occurred since 2004. A 2000 Consent Decree requires Potentially Responsible Parties to fund cleanup work, with insurance coverage guaranteeing funding through 2030.
Human exposure is currently under control, and assessments show no unacceptable human exposure pathways. Groundwater migration is not yet stabilized, physical construction is not complete, and the site has not achieved construction completion or been removed from the National Priorities List. The most recent five-year review was completed in September 2023. The next is estimated between September and November 2028.
Community members can get involved through EPA's Community Involvement Plan update, which is expected to be released in Fall 2026. Anyone interested in being interviewed for that update can contact the EPA's Community Involvement Coordinator.
