U.S. EPA orders former East Bay mine operator to take action to prevent contamination of waterway / Former Mt. Diablo Mercury Mine operator must stabilize pond containing mercury

The U.S. Environmental Protection Agency today ordered former mine operator Sunoco, Inc. to stabilize a mine waste impoundment pond at the abandoned Mt. Diablo Mercury Mine in Contra Costa County, Calif., that threatens to release mercury-contaminated waters and sediments into a nearby stream that could potentially reach the San Francisco Bay Estuary.

Currently, Dunn Creek is cutting into the berm of an impoundment pond that holds mercury-contaminated water and fine sediment. The EPA's order requires the former operator to stabilize the berm before the winter rain season begins to prevent it from collapsing, potentially causing contamination downstream to Marsh Creek and to the Marsh Creek Reservoir – which leads to the Bay.

"All too often, abandoned mines leave behind a toxic legacy that now threatens the health of people and the natural resources of the state," said Daniel Meer, the Superfund assistant director for Emergency Response, Preparedness and Prevention for the EPA's Pacific Southwest region. "This is one of many actions that may need to be taken at this site to continue to protect public health."

The mine, located on the northeast slope of Mount Diablo, is situated along the well-traveled Morgan Territory Road.

In October, the EPA sampled water and sediment for mercury contamination. The results exceeded background levels and the EPA's regulatory levels. Mercury can also be released with dust generated at the site, where airborne particulates can be deposited into the waterways as well as pose an inhalation and ingestion risk to human health.

Stabilizing the impoundment dam will mitigate the imminent threat of contaminated water and sediment from releasing at the site. Additional site assessment and characterization is needed to develop future actions to address any remaining threats posed by the former mining operations.

Mercury exposure occurs from breathing air contaminated with mercury or ingesting contaminated water and food. Short-term exposure to high levels of mercury vapors can cause lung damage, nausea, vomiting, diarrhea, increased blood pressure or heart rate, skin rashes and eye irritation. Mercury, at high levels of exposure, may cause damage to the brain, kidneys and developing fetus. The nervous system is very sensitive to all forms of mercury. Young children are more sensitive to mercury than adults.