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From the 1850's into the 1970's mercury ore was mined in the upper Cache Creek and Putah Creek watersheds. Mercury mined in this region was used throughout much of the Sierra Nevada in the gold mining process. Mercury amalgamates small particles of gold. Heating later separates the gold from the mercury. There was also some mining when needed during World War II and in the 1950's when mercury was used in hearing aids
Mined ore was heated in "retorts" (furnaces that vaporized the mercury) and then condensed. During this refining process, mercury was spilled on the ground and lost to the atmosphere. The mine tailings were dumped downhill—often directly into streams—where it conveniently eroded away in winter storms. These eroded mine tailings were deposited downstream, slowly eroding back into local creeks.
Abandoned mine sites in the upper watersheds and their legacy contamination downstream are a significant contributor to water quality impairments in our region.
Mercury is a powerful neurotoxin when converted to methyl mercury (MeHg). Inorganic mercury is converted to MeHg by bacteria in creek sediments, lakes and wetlands. The concentration of MeHg in the water column is controlled in part by the concentration of total mercury in the sediment and the rate at which the total mercury is converted to MeHg. MeHg concentrates up food chains, magnifying to levels in fish 10 million times more concentrated than in water. Eating contaminated fish can result in neurological damage particularly in pregnant women and children. This can be particularly dangerous to subsistence fishing families who rely on fish for both cultural and economic reasons.
No one knows for sure, but it seems safe to guess that there are more than 40 abandoned mines in both the Cache Creek and Putah Creek drainages. Some of the more well-known sites include Knoxville, Oat Hill, Aetna, and Helen Mines in the Putah Creek watershed and the Sulphur Bank, Abbot-Turkey Run, Wide Awake, Elgin and Petray-Rathburn Mines in the Cache Creek watershed.
Mercury ore is often formed along fault lines associated with serpentine rocks. Serpentine was originally part of the ocean crust that was hydrolyzed and thrust to the surface in the plate tectonic process. Hot liquids carrying mercury, gold and other metals traveled along the fault lines between the serpentine and other rocks to form ore bodies. Cedar Roughs, Knoxville and Walker Ridge have large serpentine rock areas.
Impaired Water Bodies and Total Maximum Daily Loads in the Region:
Section 303(d)(1)(A) of the Clean Water Act requires the California Regional Water Quality Control Boards to:
Delta Tributary Mercury Council (http://www.sacriver.org/aboutwatershed/mercury/dtmc)
Central Valley Regional Water Quality Control Board (http://www.swrcb.ca.gov/rwqcb5/)
Mine Remediation (archaeological Report)
Under Construction (Coming soon...)
Bob Schnieder, Senior Policy Director of Tuleyome, talks about mining and mercury pollution issues facing his favorite watershed, Cache Creek.