More than a century after the Gold Rush, California is still dealing with the toxic remnants of the mining industry. There are an estimated 47,000 abandoned mines in the state; some of the more heavily polluted sites are located in the Sierra Nevada foothills. Now one small community is taking action. Armed with a half-million dollar federal grant, Nevada City is cleaning up mercury, lead and arsenic that have contaminated its creek and soils.
Nevada City is home to several former industrial gold mines that operated from the gold rush through World War I. But walking through the old mine sites now, with tall oaks and pines stretching overhead and the clear Deer Creek rushing along, it's hard to believe that there are miles and miles of underground mine workings underneath.
"Locally here on the Deer Creek watershed, the main mining areas, like the Champion, the Providence, and the Mountaineer mines, have significant quantities of tailings and waste rock that are still here, they're just overgrown, and they're really not readily visible," says Jason Muir, an environmental consultant with Holdrege and Kull working on some mine land assessment along the creek.
"But when you overlay the historical maps on the property, you can see what looks like a nice meadow and a nice place for home is actually a big tailings pile."
When the mines were active, this land was covered by vast piles of silt and mine tailings, says Muir.
Now, much of it is overgrown with trees but a trained eye can still spot the contamination. Kyle Leach, an environmental consultant working on the clean-up project with the Sierra Streams Institute, points across the creek to a steep bank.
"You see that grey area there, that's pretty much un-weathered mine waste that has pretty high levels of lead in it. There's also mercury, arsenic," Leach says.
The leftover mining chemicals pervade the ecosystem here. Scientists are still trying to figure how much lead and arsenic from the environment the body actually absorbs.
Mercury levels are also quite high. But scientists say the levels in Deer Creek aren't usually a problem for swimming or drinking the water. The real threat comes from eating the fish.
"(Mercury) is a million times more concentrated -- or even 10 million times more concentrated -- in the fish than it is in the water. You'd have to drink literally thousands of liters of water to get the same amount of mercury as you'd get from eating one fish," says Charlie Alpers, with the U.S. Geological Survey.
Some of the mercury could be working its way into fish in Deer Creek, "but even more so, the bigger issue regionally is the amount of mercury that's in the particles moving downstream, " says Jacob Fleck with the USGS. "Most of the mercury is in the fine grain material, and that moves all the way to down to the Delta and San Francisco Bay."
People in Nevada City area are affected, too. For example, there are still more than 100 members of the indigenous Nisenan tribe. Many eat fish from the local streams, and still use a lot of native plants. Some Nisenan weave baskets from willow fibers.
"Some of the weavers still split the plant with their teeth, and so not just their hands, but they're bringing that right into their mouth," says Shelly Covert, the tribal council secretary of the Nisenan. "And of course there's concern for cancer in mouth, and different obvious implications from being in contact with these toxins."
There are high levels of contamination in Nevada City. The community mobilized and applied for clean up grants. It received more than half million dollars from the Environmental Protection Agency's brownfield program.
Using that money, the city contracted the Sierra Streams Institute to help with the clean-up. The group will remove some of the dirt that's highly contaminated with lead and dispose of in a toxic waste dump. In other areas they'll will cap the dirt with gravel so hikers and bikers don't kick up contaminated dust.
"And, we're going to trying to use phytoremediation, using plants to clean up mine waste," Leach said.
The group has planted some native plants that may soak up contaminants from the soil. If it works, they'll harvest the dry plant material and haul it off.
But even with all these methods combined, they won't be able to entirely clean up even this tiny parcel of land -- just one contaminated site among many in the Sierra. That's why continued research on what kinds of contamination to target is crucial.
"If you did spend hundreds of millions of dollars, would you see a difference in fish tissue concentration, or would you just be rearranging the dirt on the window and not really getting a better view," says Alpers.
Figuring out which forms of these toxins are the biggest threat to human health could help communities in the Sierra better focus their clean-up efforts, ultimately improving their environment-and their downstream neighbors.