Superfund Information Systems: Site Profile

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The 150-acre Sulphur Bank Mercury Mine site is located in Clear Lake, California. Former mining activities at the site contaminated soils, sediments and surface water with mercury and arsenic. The site also includes the Elem Tribal Colony residential area and the Herman Impoundment, a flooded open pit mine. Following immediate actions to protect human health and the environment, site investigations and long-term cleanup planning are ongoing.

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What Is Being Done to Clean Up the Site?

The site is being addressed through federal actions.

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What Is the Current Site Status?

Initial Actions: EPA removed up to 18 inches of mercury and arsenic-contaminated mine wastes from 17 residential yards at the Elem Tribal Colony in 1997. EPA backfilled the excavated yards with clean soil. In 1999 and 2000, EPA constructed surface water diversions on the mine site to prevent contaminated sediments and water from flowing into Clear Lake. A pipeline now diverts clean stormwater around the site to avoid contaminated areas. In 2001, EPA finished closing wells on the site.

Other removal actions in the late 2000s included removal of additional contaminated soil at the Elem Tribal Colony, contaminated mine waste from a nearby residential area and a road containing mine waste.

Entire Site: Remedial investigation activities for the rest of the site are ongoing.

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EPA’s Involvement at the Site

The 150-acre site was a sulfur mine from 1865 to 1871. Mining for mercury occasionally took place from 1873 to 1905. Open pit mining occasionally took place from 1915 to 1957. The mine, once one of the largest producers of mercury in California, has been inactive since 1957. About 150 acres of mine tailings and waste rock and a flooded open pit mine are located on the property. The mine tailings extend into the Oaks Arm of Clear Lake along 1,300 feet of shoreline. About two million cubic yards of mine wastes and tailings remain on the mine site. EPA's remedial investigation studies have found mercury and arsenic in the mine wastes and tailings. Mercury is present in the bottom sediments and in aquatic life in Clear Lake.

The state issued an advisory to limit consumption of fish because of high levels of mercury in fish from the lake. Clear Lake is the source of water that the Clear Lake Oaks Water District provides for municipal drinking water for 4,700 people. About 70 houses are located within three miles of the site. A freshwater wetland is located 900 feet to the north of the mine. Critical habitat for three endangered wildlife species – the peregrine falcon, southern bald eagle, and yellow-billed cuckoo – is less than a quarter-mile from the site.

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Operable Units

During cleanup, a site can be divided into a number of distinct areas depending on its complexity. These areas, called operable units (OUs), may address geographic areas, specific problems, or areas where a specific action is required. Examples of typical operable units include construction of a groundwater pump and treatment system or construction of a cap over a landfill.

View a list of all of the operable units at this site.

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Cleanup Progress

View the schedule for cleaning up this site.

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