EPA Superfund Site

SULPHUR BANK MERCURY MINE

CA | EPA ID CAD980893275

About this site’s exposure pathways: As of December 2024, the Sulphur Bank Mercury Mine site is considered Human Exposure Not Under Control. Consumption of mercury-contaminated fish from the adjacent Clear Lake is a complete pathway that poses health risks.

Site-related mercury has contaminated lake sediments in Clear Lake. Bioaccumulation of this mercury has resulted in elevated fish tissue methylmercury levels. For this reason, in 1987, 2009, 2014 and 2019, the State of California has issued and reissued a fish consumption advisory at Clear Lake. This information is distributed online and in the fishery regulations booklet provided to fishing license holders. EPA is currently pursuing increased community involvement efforts around this issue, following reports that the community is not being provided clear and consistent information around this issue.

Potential trespassers onto the mine property itself may come into contact with mine wastes and soils contaminated with mercury, arsenic, and antimony. This exposure has been limited by site controls including fencing and signage. EPA's human health risk assessment shows that a recreational/trespass scenario is an unacceptable risk due to the high levels of mercury and arsenic present in the mine waste. The risk assessment is based on exposures to youth, ages 6-17, that are most likely to recreate at the mine property.

Mine waste present in the residential areas south of the site and on the Elem Indian Colony adjacent to the site also pose a risk to human health. In 1997, 2007 and 2010 EPA completed the removal actions to excavate and cap areas of contaminated mine wastes and soils in these residential areas.

In November 2023, EPA signed a Record of Decision (ROD) for on-land portions of the site and expects a residential cleanup action as the first phase of work to begin in Fall of 2025.