Thursday, 13 June 2024

Officials monitor mercury hot spot

LUCERNE County officials have located an area near an old mercury mine along Highway 20 with elevated mercury levels, and are now conducting monitoring to watch the spot.

Tom Smythe of the county’s Water Resources Division said the area is immediately adjacent to the old Utopia Mine along the road shoulder outside of Lucerne.

The Utopia Mine was open for two years about the start of the 20th century, Smythe explained.

“We have a grant to do hot spot monitoring around the county for mercury to determine if there’s any mercury hot spots in the Clear Lake Watershed,” said Smythe.

That’s what led to the discovery of the higher mercury levels, he said.

One sample showed the presence of mercury at 17 parts per million in sediment, said Smythe, as compared to a normal mercury found in the lake’s upper arm, which measures about 1 part per million.

Smythe said the county is doing additional monitoring to try to determine how extensive the mercury is at that spot, and what it might be adding to the lake’s sediments.

“That testing is still ongoing,” said Smythe, and is located on the shoulder in the road cut.

The mine had two adits – or horizontal shafts – that came out on the shoreline, Smythe explained, and are located in Caltrans' right-of-way.

Smythe said it’s believed Caltrans plugged those shafts with concrete in the 1960s, although the agency hasn’t found the records to prove its involvement.

“We're pretty sure it was Caltrans,” said Smythe.

There is a total maximum daily load (TMDL) stakeholder group of which Caltrans is a member, said Smythe. The group looks at issues surrounding minerals affecting the lake's health. “We have been keeping this group apprised of what we've got.”

The ball may be in Caltrans’ court as far as mitigating the site, said Smythe.

On Sept. 10 the Central Valley Regional Water Quality Control Board sent a letter to Caltrans saying that Caltrans needed to submit a plan within 90 days of the letter's date to explain what they will do to address the mercury levels.

Caltrans spokesman Phil Frisbie Jr. confirmed that Caltrans received the regional water board's letter.

“We are in the process right now of performing our own soil and water testing in that area,” said Frisbie.

As soon as Caltrans has samples back, it will formally respond to the regional water board, Frisbie said – hopefully within the 90-day window.

If the tests confirm the regional water board's findings, Caltrans will have to put measures in place in order to keep the mercury from going into the lake, said Frisbie.

Frisbie said he found information online that said the mine shut down in 1908.


Smythe said Water Resources is still investigating the area, which he said is not an immediate health concern.

The area's mercury levels are minor when compared to those found at the Sulphur Bank Mine, said Smythe.

“Overall I think it's a small source of mercury,” he said.

The Utopia Mine, one of numerous mercury mines that operated around Lake County at one point, may not even be the source of the mercury, said Smythe.

It could be that it's just another area that's naturally rich in mercury and cinnabar, Smythe suggested. Because of that, they took cinnabar samples for analysis.

The area that's giving off the mercury is “pretty small,” said Smythe. The outcropping he saw was less than one square foot in size. But mercury is toxic even in small amounts, he added.

Smythe said no similar sites with such elevated levels have been found.

Mercury is naturally occurring in Lake County. Smythe said other areas, like the east end of High Valley, also have high levels of mercury, which comes up in the region's volcanic soils.

In the Coast Range, said Smythe, mercury tends to be deposited in mineral springs and associated with geothermal fluids.

Some springs still actively deposit mercury; as examples, Smythe pointed to one near the Turkey Run Mine along Highway 20 and one near Wilbur Springs in Colusa County.

Along with mercury, geothermal springs along the border of Lake, Napa and Yolo counties also deposited gold, said Smythe.

“Geologically, that's what happens,” he said.

E-mail Elizabeth Larson at This email address is being protected from spambots. You need JavaScript enabled to view it..


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