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Source of Nevada County’s South Yuba River plume remains a mystery

The water may have cleared, but the reasons the South Yuba River turned a sediment-filled yellow and registered an alarming level of E. coli remain murky.

The plume of contaminated water was initially spotted Sept. 20, quickly prompting a no-swim advisory. Then county officials pointed to a property in the 13000 block of Kilham Mine Road as the potential source of the contamination.

That’s since been ruled out, a state water official said.

Andrew Altevogt, assistant executive officer of the Central Valley Regional Water Quality Control Board, said his agency’s staff went three times to the area, inspecting and taking water samples.

“We’ve been trying to figure out what happened and what exactly went into the water,” he said Tuesday. “The (Kilham Mine Road) property does not look like the source at this point.”

Altevogt said his agency is still actively investigating and added its most recent test results showed no chemicals of concern.

“We will continue to work with the county,” he said, noting that access to the area is difficult. “We do want to find out what happened.”

Nevada County Environmental Health Director Amy Irani said the county will defer to the state’s investigation, although she speculated that historic mining might have led to a wash of dirt into the river.

According to Irani, the county had “absolutely” ruled out any cannabis-related activity as the cause.

Irani said her department had just compiled all its test results and given the river a clean bill of health.

“The water quality throughout (the test sites) has been testing at drinking water levels,” she said. “There is no arsenic, no mercury, no lead — those were the things I was focused on that were of concern.”

County officials did find several code violations on the property, county spokeswoman Taylor Wolfe said. She would not be specific as to what was on that property, however, citing the ongoing investigation.

In the wake of the river scare, South Yuba River Citizens League volunteers will increase their own water testing, said Executive Director Melinda Booth.

SYRCL already does “safe to swim” E. coli testing at all major river crossings throughout the summer. Booth said.

“They usually come back fine,” she said. “It’s very rare to have even a slightly elevated count.”

SYRCL now has decided to increase its monitoring efforts to include testing through the first rains of the season, Booth said.


Several agencies gathered in the wake of the plume’s discovery.

Nevada County staff, the South Yuba River Citizens League, California State Parks and Nevada County Consolidated Fire District met Sept. 20 to discuss current river conditions, and officials from Nevada County Environmental Health went to various South Yuba River locations to take water samples for testing.

While results were pending, the county decided to issue a no-swimming advisory for the river, from below the town of Washington to Englebright Lake, due to the high level of sediments of unknown origin. The next day, the county extended the advisory to Englebright, and reported finding E. coli levels at double the safe recommended levels by the Environmental Protection Agency. Testing also was done for toxic metals such as arsenic, lead and mercury, reports stated.

By Sept. 24, the no-swim advisory was lifted after tests showed E. coli levels — previously found at dangerous levels near the Highway 49 bridge — had significantly dropped. Tests for toxic metals for mercury, lead, copper, arsenic and aluminum also showed safe levels for recreation.

To contact Staff Writer Liz Kellar, email lizk@theunion.com or call 530-477-4236.


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