This week, scientists from state and federal agencies landed on a sand bar where Humbug Creek and the South Yuba River converge to learn more about a mercury hot spot located downstream from the largest hydraulic mine site in the Sierra Nevada.
The study will examine what type of mercury is in the sediment of the Yuba River watershed and how readily the liquid metal changes into a harmful form known as methylmercury. Aquatic life, including fish consumed by humans, accumulates the poison.
"This is all new science. Nobody's done this before," said David Lawler, who is leading the South Yuba Mercury Study, also known as the Humbug Project, for the Bureau of Land Management. The federal agency manages a 7-mile stretch of the river between Edwards and Purdon crossings.
"This is the first intensive sediment sampling in the area," said Charles Alpers, research chemist for the California Water Science Center for the U.S. Gelogical Survery. In the past, multiple agencies have sampled mercury in fish and water, Alpers said.
Mercury is poisonous for the nervous system when ingested in its methyl state but does not pose risks to swimmers or drinking water, Lawler said.
Lessons learned about how mercury reacts when it becomes oxygenated could impact regulations of suction dredge mining, a popular recreation and livelihood for hundreds of people with mining claims along many rivers in the state.
Increased regulations worries Mark Hale, a Grass Valley resident since 1982. He understands the need to protect human health but also feels strongly about preserving mining and timber traditions in Nevada County.
"I don't want to see us lose the right to dredge, but I believe that's the way it's going," Hale said, adding he fears mercury risks could lead to a closure of public lands.
Earlier this summer, the state water board halted a pilot study by the Bureau of Land Management using suction dredge equipment to recover mercury from sediment in the South Fork Yuba River. That project was stopped because of concerns that a small percentage of mercury is lost to the environment and could pose risks to aquatic life.
"Everyone acknowledged if they dredged mercury here they were going to release some downstream. You want to come up with a cleanup method that doesn't cause more problems," said geologist Rick Humphreys with the state Water Resources Control Board.
"Is there really enough gold in these rivers to justify dredging operations?" Lawler asked.
Miners argue that all the blame can't be directed at them and that winter storms release small amounts of mercury into watersheds every year.
Two professional gold miners " Ken Eddy and Dale Carnegie from the Happy Camp area on the Klamath River " were contracted to help search for mercury in the Yuba, found in sediment lodged in cracked rocks submerged beneath the water. Losing the ability to dredge would be financially disastrous to old-time miners, they said.
"Dale makes his living on this. There's a lot of miners who depend on gold," Eddy said.
Waterways loaded with poison
On Monday, a helicopter made seven trips transporting gear and heavy equipment to the area accessed by a steep, three-mile hike on the Humbug Trail.
On Thursday, experts from the BLM, USGS and Water Resources Control Board were on hand.
Throughout the week, crews have been digging test pits by hand on the shoreline, extracting tons of sediment and processing hundreds of pounds of the dry river bed.
They sifted gravel-sized to fine clay sediment through a series of graduated metal sieves, then contained the samples for shipment to a lab for more analysis.
"There's a little mercury in everything," Alpers said. Tiny flecks of found gold and amalgam of mercury gleamed from glass vials at the outdoor work station.
In recent years, more than 100 pounds of mercury have been found in the area by recreational dredgers, Lawler said.
For nearly 30 years during the height of hydraulic mining at Malakoff Diggins, 40 million cubic yards " more than a cubic mile " was processed and washed down an 8,000-foot-long tunnel to Humbug Creek and the South Yuba, Lawler said.
Ten pounds of mercury was used for every linear foot of sluice box, or about 80,000 pounds per year, Lawler said.
"They used hundreds of thousands of pounds of mercury" to capture the gold, he said.
It is estimated that 10 to 30 percent of that " or one quarter million pounds of mercury " was lost into the waters of the Yuba, Lawler said.
No one knows how much is still there.
The Yuba River flows downstream until it joins the Feather River, which empties into the Sacramento River and eventually to San Francisco Bay. Traces of mercury have been found in fish throughout the system.
"That is what we are concerned with. It's a very complex food web," Lawler said.
"By the time it's a water skeeter to a frog, (the mercury concentration) gone up 5,000 times," he said.
Seven reservoirs in the Sierra Nevada and foothills have health advisories for fish, including Lake Combie, Scotts Flat Reservoir and Englebright, Lawler said. Many reservoirs were built during the Gold Rush era to store hydraulic mine tailings, Lawler said.
To contact Staff Writer Laura Brown, e-mail email@example.com or call 477-4231.