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Nevada County confirms Kilham Mine Road property not source of South Yuba River plume

Nevada County has released the results of a state water board investigation into the mysterious yellow sediment plume that closed off the South Yuba River in September.

A historic mine property on Kilham Mine Road, initially targeted as the suspected source of the discharge, was cleared by the Central Valley Regional Water Quality Control Board in late October. But according to Nevada County Environmental Health Director Amy Irani, the water board investigation is ongoing.

“They continue to work towards pinpointing the source of the plume, and will investigate 2 miles upstream from the Kilham Mine Road location … on Bureau of Land Management property along the South Yuba River,” a press release stated.

The plume of contaminated water was initially spotted Sept. 20. That day, Nevada County staff, the South Yuba River Citizens League, California State Parks and Nevada County Consolidated Fire District met to discuss the river conditions, and officials from Nevada County Environmental Health went to various South Yuba River locations to take water samples for testing.

The county issued a precautionary no-swimming advisory for the river due to the high level of sediments of unknown origin. The next day, the county reported finding E. coli levels at double the safe recommended levels by the Environmental Protection Agency. The no-swim advisory was lifted Sept. 24 after tests showed E. coli levels had significantly dropped. Tests for toxic metals for mercury, lead, copper, arsenic and aluminum showed safe levels for recreation, county officials said.

State water board investigators made several visits to the Kilham Mine Road property, a historic mine site known as Blue Tent Diggings. County Environmental Health staff members took surface water and soil/sediment samples through Sept. 29, none of which showed toxic metals or high levels of E.coli.

On Oct. 23, the state water board submitted a report that found no evidence of a sediment discharge from the property matching the characteristics of the plume. The report did note land disturbances and code violations that included three graded areas and regrading of an access road. The property owner was required to enroll under the Construction Storm Water General Permit and stabilize the disturbed areas at the site.

According to the county’s press release, the state planned to conduct fly overs of the area after the first significant rain fall, and the county will continue to work with both the water board and local organizations SYRCL and Sierra Fund on the investigation to find the source of the plume.

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

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