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EPA, STATE CLEAN UP ABANDONED MINE THAT THREATENED TOMALES BAY ECOSYSTEM

Release Date: 11/1/1999
Contact Information: Leo Kay, U.S. EPA, 415/744-2201, Will Bruhns, RWQCB, 510/622-2327

     Mercury No Longer Rising
                                 
     SAN FRANCISCO -- Federal and state officials gathered in West Marin County today to celebrate a recently completed $3 million cleanup of an abandoned mine that had been leaking mercury into Tomales Bay.

     In the past 20 years, an estimated 170 pounds of mercury-contaminated sediments had eroded from the site and discharged into Gambonini Ranch Creek, which drains to Walker Creek and in turn Tomales Bay.  Tomales Bay supports a multi-million dollar oyster industry, and is considered one of the most pristine estuaries on the West Coast.

     "We can now say that the mercury is no longer rising. Great teamwork by the state and federal government prevented future damage to oyster beds and other local wildlife in one of the state's most pristine waterways," said U.S. EPA Regional Administrator Felicia Marcus.  "The steep canyon walls and rainy winters made this a difficult site to clean up, but we persevered and got the job done."

     "Tomales Bay, because of its nearly natural condition, is a rare and valuable resource for the Bay Area.  The Gambonini Mine posed a major threat to the bay. The State of California and US EPA have removed this significant environmental and public health threat in an expeditious and cooperative effort. We are extremely proud of this partnership." said Pamela Lloyd, member of the San Francisco Bay Regional Water Quality Control Board.

     "This remediation project highlights a state/federal partnership in resolving environmental impacts from mining operations", said Nancy Sutley, deputy secretary of CalEPA.

     Over the course of two field seasons, work crews:

          Used heavy equipment to cut 200,000 cubic yards of dirt from the top of the hill to serve as a  wedge at the base of the hill to prevent landslides and other erosion.  A small portion of the material was placed in the mine pit.

          Installed more than 3,000 lineal feet of subdrains to capture groundwater within the re-engineered hillside.

          Constructed a drainage system to prevent erosion and to minimize sediment discharge.

     The Regional Water Quality Control Board will soon begin planting hundreds of willow trees on the engineered hillside in order to prevent future erosion at the site.  The board will also restore channels that had been damaged on the site.

   The Gambonini Mine Site encompasses roughly 16 acres, including a two acre mine pit and 11 acres of mining wastes that were dumped down a steep canyon adjacent to the pit. From 1964 through 1970 the Buttes Gas and Oil Company mined and processed cinnabar (mercury ore) on land that was leased from the site's current owner.  A tailings dam that mine operators had built when closing down the mine failed in 1982, inundating nearby Gambonini Ranch Creek with mining waste.

     By 1990, the Gambonini Ranch Creek was cutting through the toe of the mining waste pile and draining into Salmon and Walker creeks.  The Regional Board requested EPA assistance last year after continuous sampling showed elevated levels of mercury in Gambonini Ranch Creek.  Samples indicate that commercial oysters in Tomales Bay have not been impacted by discharge from the site.