A superfund site.
The Sulphur Bank Mercury Mine site is located at the southeastern end of the Oaks Arm of Clear Lake. The Superfund site also includes the Elem Tribal Colony which is located directly adjacent to the mine property. Approximately 70 houses are located within 3 miles of the site. A freshwater wetland is located 900 feet to the north of the mine. A critical habitat for three endangered wildlife species, the Peregrine Falcon, Southern Bald Eagle, and Yellow-Billed Cuckoo, is less than 1/4 mile from the site.
The 150-acre Sulphur Bank Mercury Mine site initially was mined for sulfur from 1865 to 1871. Mercury ore was mined intermittently by underground methods from 1873 to 1905. The site was intermittently open pit mined from 1915 to 1957. The mine, once one of the largest producers of mercury in California, has been inactive since 1957. Approximately 150 acres of mine tailings and waste rock and a flooded open pit mine (called the Herman Impoundment) are located on the property. The mine tailings extend into the Oaks Arm of Clear Lake along 1,300 feet of shoreline. Approximately two million cubic yards of mine wastes and tailings remain on the mine site. The Herman Impoundment, which is filled with acidic water, covers 23 acres to a depth of 90 feet and is located 750 feet up gradient of the lake. EPA's remedial investigation studies have found mercury and arsenic in the mine wastes and tailings. Mercury is present in the bottom sediments in Clear Lake, and mercury has bio-concentrated in the food web of Clear Lake. The levels of mercury in fish from the lake led the State to issue an advisory to limit consumption of fish. Clear Lake is the source of water that the Clear Lake Oaks Water District provides for municipal drinking water for 4,700 people.
Source: US EPA Region 9 Superfund