An abandoned mercury mine that scientists fear could poison life in Walker Creek and Tomales Bay may finally get cleaned up, state officials having removed roadblocks so the project can begin.
Next month, the San Francisco Bay Regional Water Quality Control Board is expected to select engineers for stabilizing a hillside packed with mercury-laced mine tailings.
The 11-acre mine site is at the Gambonini Ranch on the Marshall-Petaluma Road.
The cleanup is intended to keep the toxic mineral from eroding into a tributary of Walker Creek called Arroyo Sausal and contaminating the bay seven miles away. Work is expected to begin in May, said Dyan Whyte, a regional board engineer and geologist.
Allowing the cleanup to start is the settlement of a lawsuit against the mining company, Texas-based Buttes Oil & Gas. Water Quality Control officials said the settlement means the regional board can release $569,000 in state funds - held since 1993 - for the cleanup.
Under terms of the settlement, Texas-based Buttes Oil & Gas Company agreed to pay $128,000 toward cleanup costs, regional officials said.
Buttes leased the mine site from the Gambonini family and removed more than $1.63 million of quicksilver from the site in the 1960s.
When it abandoned the mine and capped it in 1970, Buttes was lauded by the Marin Conservation League as an example of what a responsible mining company could do. Unfortunately, the 100-year storm of 1982 uncovered the mine's tailings pile.
Agreements have also been reached between the state and landowner Alvin Gambonini. The agreements hold the state liable for the project while Gambonini is responsible for monitoring the site after its cleaned up, Whyte said.
"I have never had a problem [getting] access [to] the property for taking samples," Whyte said, adding that she thought Gambonini had valid concerns about liability and what would take place on his ranch.
Gambonini told The Light Wednesday that until recently he was being held financially responsible for the cleanup, liable for injuries for cleanup crews, and damages if the cleanup failed.
Gambonini also said he believes the state is wasting money because the tailings hill is already stable, especially if tires and trees are thrown into two 30-foot gullies to stop a slide created by the 1982 storm.
"There is a three-foot culvert behind the barn that's been there since 1940," Gambonini said. "The only time it plugged up was in 1982."
Nonetheless, with a written agreement now in hand, Gambonini said he really has no choice but to allow the cleanup.
Now gauges are set up to regularly monitor Walker Creek for any mercury and sediments from the mine. The data will help engineers develop mitigation measures and later determine if the cleanup was successful, Whyte said.
After identifying the site in 1989 during an investigation of abandoned mines, Whyte in 1993 took samples of water coming from the tailing piles.
The samples contained up to 2,500 times the mercury level considered hazardous to human health. Another sample taken a mile downstream on Salmon Creek (the headwaters of Walker Creek) showed levels 100 times higher than Water Quality Control Board standards.
Samples of water from Soulajule Reservoir, which is upstream from the Gambonini ranch on Arroyo Sausal, found very low, non-hazardous levels of mercury, Whyte said.
While the old mine adds mercury to Walker and Salmon creeks, the surrounding hills, which are rich in mercury, also contribute to elevated - but not dangerous - levels of mercury in Tomales Bay, said Tim Hollibaugh, senior research scientist with Center for Environmental Studies, a state university field station.
From a base at Marconi Cove, the center has surveyed the bay since 1987, and so far there is no evidence that the mercury has affected the number or variety of species in the bay or the creek, said Hollibaugh, a water chemist and biologist.
But the risk of poisoning still exists should increased mercury-laden sediments enter the bay, he said.
"If this [mine-tailings erosion] was allowed to continue, there could be a massive [landslide] where mercury-laden sediment could be washed into the bay in one slump," Hollibaugh said.
Mercury can be absorbed by microorganisms and converted into a form eventually eaten by clams, fish, and humans, he said. Prolonged exposure to mercury can cause gum disease, neurological disorders, and mental disturbances.
Richard Plant, a director of the Point Reyes Station-based Resource Conservation District, said his district previously planned to spearhead the cleanup, but the RCD no longer has funds available.