Sulphur Bank Mercury Mine is a 160-acre abandoned open-pit mine on the shore of Clear Lake in Lake County, California. It operated intermittently from 1865 to 1957, extracting sulphur and mercury. Those operations left about 2.5 million cubic yards of mine waste behind. The site was added to the National Priorities List in 1990 and cleanup is actively underway.
The main contaminants are mercury, arsenic, antimony, and thallium. Mercury and arsenic appear in both soil and groundwater. Antimony and thallium are found in soil. Stormwater and groundwater leaving the site have carried mercury into Clear Lake, where it has built up in sediment and accumulated in fish. A fish consumption advisory has been in place since 1987. Swimming in Clear Lake is considered safe, as mercury levels in the water consistently fall below government standards. Human exposure at the site is not currently under control, and groundwater migration is not stabilized.
EPA has carried out several short-term cleanup actions over the years. These include shoreline erosion control, removal of contaminated soil from 17 residential yards at the Elem Indian Colony in 1997, construction of surface water diversions between 1999 and 2000, closure of geothermal wells in 2000 and 2001, and removal of 28,000 cubic yards of mine waste from the Elem Indian Colony between 2006 and 2008. Additional work addressed contamination along nearby roads, and sediment capping tests were conducted in Clear Lake between 2014 and 2016. The site is divided into four operable units. EPA finalized a cleanup plan for the terrestrial mine site and residential soils (Operable Unit 1) on November 9, 2023, after a 90-day public comment period that included online sessions, open houses, and public hearings. Active remediation began in September 2024 and construction is estimated to finish between December 2027 and February 2028. Cleanup of Clear Lake sediment (Operable Unit 2) and the North Wetlands (Operable Unit 4) are at earlier stages, with a record of decision for the North Wetlands anticipated between September and November 2028.
To protect yourself and your family, do not enter the mine site. It is private property and contains both physical and chemical hazards. Follow California's Clear Lake Fish Advisory for safe consumption limits on fish caught in the lake.
For questions or to get involved, contact the EPA Community Involvement Coordinator assigned to this site. EPA is also updating its Community Involvement Plan and welcomes public input through community interviews.
