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Mercury Up the Creek
A pick and a gold pan, the tools of the prospector's trade, firmly embedded in California mythology. What's usually left out of the picture is a good supply of mercury, used by early prospectors and their successors to amalgamate gold and make it easier to recover. For more than 50 years, from the 1880s until after World War I, mercury was mined throughout the Coast Range for use in gold mining and processing. Today, the mercury mines are abandoned and, until recently, more or less forgotten.
Now however, findings of high mercury levels in Cache Creek and its tributaries are reinforcing suspicions that mines are a big source of mercury inputs to the Estuary and sparking an ambitious new watershed protection program for the creek's watershed, a 1,150-square-mile expanse reaching from the Indian Valley Reservoir to the north and Clear Lake to the south and draining into the Sacramento River ten miles south-east of the state capital.
"We were pretty much floored when we got the data," says the Central Valley Regional Board's Bill Croyle of water samples taken as part of the Bay Protection Toxic Clean-up Program in January 1995. During a peak storm period, mercury levels at the creeks' outfall at the Yolo Bypass (near the site of the biggest wetland restoration projects west of the Mississippi), were measured at 695 parts per trillion. The EPA water quality criteria is 12 parts per trillion total mercury.
During the rest of that winter and the next, Board scientists tracked the mercury levels into the watershed, identifying the tributaries with the highest mercury loads. "The tributaries with known mine sites on them are coming out very hot," says Croyle, "but we don't know for sure that they're the source. We are also looking at suspect natural geological formations." Croyle notes that low concentrations of mercury exist in highly erodible soil throughout the creek's watershed. "What we do know now is that Cache Creek it a major source of mercury in the Delta during high flood events." Indeed, mercury from watersheds like Cache Creek may be making its way as far down the Estuary as the Bay, where it's been found both in sediments and in fish at levels high enough to change state health warnings for fish consumption in 1995.
This winter, the Board hopes to pinpoint precisely where the mercury loads are coming from. For the moment suspicions focus on about 10 large mines with open portals and waste dumps and on several natural sources. In the meantime, the Board's awaiting the results of studies by U.C. Davis biologist Darell Slotten which should show how much of the mercury is biologically available for uptake by estuarine organisms.
The mercury findings, the latest in a series of environmental problems that have plagued Cache Creek in recent years, highlighted the need for a comprehensive watershed management plan. Enter the Colorado Center for Environmental Management, which has developed a promising waste clean-up program for a Colorado watershed riddled with abandoned mines and has received an EPA grant to replicate its methods in other states. According to the Center's Todd Bryan, "We were looking for a project that involved mines as well as an opportunity to do a watershed approach to collaborative decision-making." The Center chose Cache Creek for its first project under the grant, and obtained additional funding from California's Hewlett Foundation.
Despite the initial focus on mercury, Bryan notes that this may not turn out to be the priority of the watershed program. "What we do is bring a structured framework by which stakeholders can identify problems and develop common strategies for addressing them. As we open up the process we may come up with different ideas about what its ultimate goals are," he says.
One issue that's sure to figure largely in discussions is the long-running debate over whether to permit deep-pit off-channel gravel mining to replace the in-channel mining that has decimated the creekbed. Some mining opponents fear that mercury will collect in the groundwater-filled pits, threatening the food chain and perhaps seeping into the drinking water supply. Two measures on the November ballot address gravel mining issues, including where mines could be located, how deep they could be, and what water quality monitoring would be required. In the meantime, the Yolo County Department of Public Health is planning a mercury monitoring program focusing on drinking water.
One of the two ballot measures requires mining companies to provide funding for restoration of abandoned in-channel gravel mines. According to Jim Eagan of the Yolo County flood control district, these pits could have several beneficial uses, including riparian habitat restoration and groundwater recharge. The Army Corps has conducted a reconnaissance study of the pits and determined that there is a federal interest in participating in their restoration. However, a feasibility study is on hold pending the outcome of the election.
In addition to mercury and gravel mining, other issues that will likely figure in the watershed negotiations include pesticide use by stone-fruit growers in the lower part of the watershed, and algae problems in Clear Lake. As for the abandoned mercury mines, if they do turn out to be a major source of mercury several difficult issues will need to be addressed, beginning with determining liability. State agencies have already had problems when they tried to staunch metal runoff from abandoned mines and found themselves held liable for inadequate clean-ups. Nevertheless, says the Board's Jerry Bruns, "We sort of hope the high mercury loads are coming from mines, so we only have a couple of big sources to deal with."
Contact: Bill Croyle (916)255-3091
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