Bottoms up

Gold-mining technology keeps mercury out of foothill fish

Dredging for a mercury solution at Combie Reservoir.

Dredging for a mercury solution at Combie Reservoir.

Photo By PHoto by Carrie Monohan

A Gold Country irrigation district has discovered an innovative way to keep mercury out of fish, but now needs to reel in funding to bring the project to other waterways.

Tested as a pilot project at the Combie Reservoir and nearby Bear River, the process involves dredging sediment from the waterway through suction. Mercury is then removed by centrifugal force, which separates it out through spinning.

“The Nevada Irrigation District has not removed any sediment at this point in time,” said Carrie Monohan, science director with The Sierra Fund, who’s advising on the project with the Nevada Irrigation District. “The project is to remove 200,000 tons over 3-5 years which may begin next year if we get funded.”

A toxic legacy of long-ago gold mining, (see “Toxic trails,” SN&R Green Days, August 12) mercury is now found in many Sierra waterways, where it is converted by bacteria to methylmercury. (In a report this year, the Sierra Fund also said toxic minerals are prevalent in many Gold Country recreation areas.) The mercury is then consumed by plankton and in turn eaten by fish, which concentrate the metal in high amounts. At the top of the food chain, humans, who eat affected fish, then become vulnerable to related health hazards.

According to California’s Office of Environmental Health Hazard Assessment, those who consume affected fish can in time have subtle health problems, varying from blurred vision and poor coordination to heart and kidney disease.

“Pregnant woman and children are most vulnerable,” Monohan told SN&R. For that population, OEHHA recommends eating freshwater fish just once a week.

At a Sierra Fund conference this month, speaker Dr. Jane Hightower also said that exposure to small amounts of mercury can cause chronic health problems.

Like many fishing expeditions, the pilot project at Combie Reservoir near Meadow Vista began with a snag.

Ron Nelson, general manager of NID, explained that the district was already dredging debris to make room for more water storage. State water authorities then expressed concern that mercury disrupted by the dredging would affect water quality. In response, NID turned to a Canadian gold-mining company that had a device to extract gold from river rock. Instead of gold, NID and the company used the equipment to separate out the mercury.

“It was innovation borne of necessity,” said Nelson, who added that the sediment is sold to commercial rock quarries and the mercury is sent to a disposal site.

With enough funding, the NID initiative could also provide a solution beyond the Combie Reservoir in Nevada County. The district is now seeking federal and state grants to help cover the $9 million cost of the project and is working with Sen. Dianne Feinstein to secure congressional appropriations.

In the meantime, Monohan said efforts are also underway to improve posting of health advisories at fishing sites.

“There have been very few advisories [posted], so there has been a big effort to change that,” Monohan said. “They especially need better signage at sites that are most visible to anglers.”

More long term, NID and the Sierra Fund hope to attack the problem from the bottom up.

“It’s very much at the experimental stage,” Nelson said of the mercury-extraction project. “But we would like to see if it could work at other reservoirs, in the state and elsewhere, as well.”