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DTSC Oversees Environmental Cleanup of Mercury-Contaminated Park

Each spring, California wildflowers create a bright carpet of color inside the beautiful Almaden Quicksilver County Park in Santa Clara County.  It’s hard to imagine that 135 years ago this magnificent 4,000-acre setting near Silicon Valley was home to mercury mining. The old mines left an ugly mark. Waste piles scarred the landscape.

With oversight of the Department of Toxic Substances Control, a cleanup of mercury waste restored an open space that can be appreciated by all Californians.

“The park was the site of the largest-producing mercury mine in North America,” said Barbara Cook, Acting Assistant Deputy Director for DTSC’s Brownfields and Environmental Restoration Program. “This wonderful park would probably still be a continuing source of mercury contamination if DTSC didn’t oversee this cleanup.”

Miners processed mercury on the property for more than 100 years beginning in 1845. Mercury was still there in the 1980s when the California Department of Health Services began soil sampling.  DTSC began overseeing investigations and cleanup after Santa Clara County bought the property for use as a park.

When DTSC began its cleanup, mercury-containing waste from the mining operation still disfigured the landscape. Evidence indicated that mercury waste had eroded into nearby creeks and reservoirs, which flow into the Guadalupe River. Tests in 1986 showed that 69 percent of fish sampled in the river contained levels of mercury above those considered safe for human consumption. Another development complicated the cleanup: Areas around Alamitas Creek were home to the red-legged frog, a federally listed threatened species. DTSC worked with the California Department of Fish and Game and the U.S. Fish and Wildlife Service to protect the frogs and their habitat during the cleanup.

In the end, thousands of tons of contaminated soil were removed from the property. Santa Clara County covered waste piles with soil in five areas of the park. The county built a 1,500-foot wire mesh and rock barrier on the bank of Alamitas Creek to prevent runoff. Today, DTSC regularly inspects the solutions to be sure they remain in good shape.

Mark Piros, former Almaden cleanup project manager, and now a Berkeley-based unit chief for DTSC’s Cleanup Program, says, “The remediation completed at the park provides assurance that visitors can safely use the park without coming into contact with mercury-containing wastes. And it protects the nearby streams that are tributaries to the Guadalupe River from further mercury impacts.”Santa Clara County officials say they’re equally pleased.  “The County of Santa Clara is proud of its efforts to remediate nearly all of the man-made pollution from over 100 years of mining at Almaden Quicksilver County Park,” said Mohamed A. Assaf, P.E. Senior Facilities Engineer with the county’s Parks and Recreation Department. “Residents now have a beautiful park to enjoy that is full of history and natural wonder.”

Almaden Quicksilver County Park, with its miles of trails, is used mostly for hiking, biking and horseback riding.  More than a decade after its cleanup, the park is a haven for outdoors enthusiasts and wildlife. The beauty of the park and its popularity are a striking reminder of cooperative work by DTSC, Santa Clara County and other state, local and federal agencies. Collectively, they made possible a spectacular new recreational environment that millions of area residents will enjoy for years to come.