On October 11, 2017, The Sierra Fund’s Science Director Dr. Carrie Monohan presented to staff of the CA Department of Conservation as part of their Brown Bag Lunch Series, which features both internal and outside speakers on a range of topics. Dr. Monohan’s presentation addressed Gold Rush-era sources of mercury and sediment, namely abandoned mines and downstream reservoirs.
During the California Gold Rush, more than ten million pounds of mercury were applied at mining operations to aid in gold recovery. 10 to 30 percent of this mercury was lost to the environment, posing a threat to ecosystems and public health today.
The storm runoff from the Malakoff Diggins hydraulic mine discharges into nearby creeks, contributing significant loads of sediment and mercury as it flows into the Wild and Scenic South Yuba River. Mercury-contaminated sediment accumulates in reservoirs, and the Nevada Irrigation District’s project to remove this material from Combie Reservoir on the Bear River is an innovative approach to addressing legacy contamination.
Dr. Monohan discussed how our state can address mercury left over from the Gold Rush, and explored strategies and the multiple benefits associated with removing contaminated sediment to restore reservoirs across the Sierra Nevada. She was slated to give a similar presentation earlier in the week at Sierra College’s Science Speaker Series. That event was cancelled due to the unfortunate circumstances associated with wildfires in Nevada County. Stay tuned for a rescheduled date, likely in the spring.