Local waters are now being tested for the toxic legacy of the area's Gold Rush history.
Carrie Monohan and Rosemary Gregor hiked under a steady drizzle Wednesday near old mining sites on restricted Nevada City public land. The two researchers tramped through thorny bushes so they could get to the banks of Deer Creek and sample sediment flowing in the muddy water.
The pair was working for Friends of Deer Creek. Their goals include garnering grants for any needed cleanup, such as removing highly contaminated sediment, so the land can be used for recreation.
"Everybody's thinking about this now," Monohan said about mercury contamination. "It starts with sound science."
Grass Valley and Nevada City contain many old mining sites, which are frequently associated with high levels of mercury and other poisonous metals. However, little evidence has been gathered locally about the lingering presence of such toxins.
Mercury was widely used by miners to locate gold. They poured the substance into sluice boxes, where it latched onto gold and sank both elements to the bottom. Although miners burned off the mercury that amalgamated to gold, an estimated 20 to 30 percent of it drained into rivers, streams and soil.
Old records and lithographs of former mines now help guide the scientists to potentially high concentrations of mercury, arsenic and lead, all used by miners to hunt for gold. Agencies such as the Bureau of Land Management are working with Friends of Deer Creek on the project, for which Nevada City was awarded a $200,000 grant from the United States Environmental Protection Agency.
Builds up in food chain
The main danger of mercury left over from mining is its ability to build up in the tissues of animals as they go up the food chain - called bioaccumulation.
Bacteria pick up heavy metals from the sediments, passing the toxins up the chain to fish and birds.
People who eat a lot of mercury-contaminated fish risk damaging their central nervous systems and passing on birth defects to their children.
Despite that danger, few signs are posted around Deer Creek warning any would-be fishermen of the danger.
"There's really not very much data," Friends of Deer Creek Biologist and Director Joanne Hild said about mercury levels at places like the old Providence Mine site near Deer Creek. "We know we have to do more."
At the Friends of Deer Creek laboratory on Main Street in Nevada City, scientists peered through microscopes at insects collected from the creek, which could contain evidence of mercury contamination. Initial results from this year's tests are expected in several months.
To contact Staff Writer Josh Singer, e-mail email@example.com or call 477-4234.