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Hazardous spill at Hwy 49 sinkhole

The sinkhole appeared last December after four days of torrential rain created a leak in a culvert that spurred the sudden appearance of a sinkhole.
File photo |

The sinkhole that formed near Highway 49 last December continues to be a thorn in the side of Caltrans.

A potentially hazardous material known as styrene leaked from the area where a Caltrans contractor was attempting to repair the culvert responsible for creating the sinkhole, said Peggy Zarriello, interim director of Nevada County Environmental Health.

The hazardous material leak was initially detected on July 22 by a resident living near the culvert, who noticed a foul odor emanating from the site, Zarriello said.



“When the material hits the air and volatilizes, it stinks,” she said.

The leakage has been contained to a 450-foot area surrounding the culvert, located beneath Highway 49 between Alta Sierra and Grass Valley.




Styrene is a resinous material used in engineering projects to plug leaks in areas that are difficult to reach, said Steve Nelson, a Caltrans spokesman.

Stewart Engineering Inc., based in Redding, used the material in an attempt to fix a portion of a culvert damaged at the end of last year.

When the culvert sprang a leak after four days of relentlessly torrential rain early last December, water leached into an area just off the shoulder of Highway 49, creating a large sinkhole, the depth of which was never fully determined, according to previous reports.

Caltrans contracted with Stewart to perform emergency repairs and reline the culvert to avert any exacerbation of the existing sinkhole or cause similar problems in the area.

“It’s a preventative project,” said Caltrans spokeswoman Rochelle Jenkins.

The contractor elected to use styrene to seal a section of the pipe that was farther underground and more difficult to reach.

Styrene was initially applied in liquid form and was designed to congeal and solidify in place with the assistance of a large balloon, Jenkins said.

For unknown reasons, the polymer did not harden and instead seeped out from the culvert, draining into the soil and a slender run-off creek that serves as a tributary to Wolf Creek, Zarriello said. The contamination plume was restricted to the immediate vicinity surrounding the construction site and no chemicals reached Wolf Creek, she said.

Workers with Stewart Engineering are on site currently in an effort to clean the affected portions, and further tests are under way to determine if any contamination remains, Zarriello said.

Test results should be available by Friday, Nelson said.

Stewart Engineering is diverting the small stream into Banker tanks to prevent any possible contamination from entering Wolf Creek, Zarriello said.

Caltrans is seeking a permanent solution for sealing the culvert, Nelson said.

The agency will continue to monitor the soil and water quality until it is determined the hazardous material is not merely contained but also cleaned up, Jenkins said.

Cost estimates are not available for the clean-up portion of the project as the priority remains remediation, she said.

The transportation agency has yet to determine the cause of the material leak at the site.

The sinkhole itself has been stabilized and does not pose a danger to the public, Jenkins said.

To contact Staff Writer Matthew Renda, email mrenda@theunion.com or 530-477-4239.


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