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Hydraulic gold mining began in 1853 in the Sierra Nevada of California. Early efforts were not very prosperous until the mining process was revolutioned and became more efficient. Hydraulic mining involved aiming jets of water at a mountainside through nozzles. The tremendous pressure of the water caused the side of the mountain to wash away. gold-bearing sediment from the mountain was then run through a large sluice. These sluices were lined with liquid mercury (quicksilver), which was used to capture the finer gold particles. The remaining debris was washed into nearby streams and rivers, and a portion of it eventually made its way to San Francisco Bay.
Hydraulic mining removed over one billion cubic meters of sediment from the foothills of the Sierra Nevada during the gold rush. It has been estimated that over 10,000 tons of liquid mercury was lost to the watershed during this time. Questions remain about how much of this mercury-contaminated sediment remains in the Bay, where it is located, and whether it is a potential threat to Bay wildlife and human health.
Our group is currently studying the present-day distribution of mercury-contaminated hydraulic mining debris in the North Bay. We are also cooperating with USGS researchers to study mercury levels and the bioavailability of the mercury in the debris.
Because of the devastation and damage caused by the influx of this debris to farms and towns downstream from the mining, hydraulic mining was banned in 1884. The photo shown at the right is titled Parks Bar, taken by G.K. Gilbert in 1908. It shows how mining debris clogged waterways, even after hydraulic mining practices had ceased.