Studies judge dredge
January 27, 2011
Fans – and foes – of suction dredge mining will have to wait a little bit longer to find out whether a ban instituted in 2009 will remain in effect.
But the findings in two studies the U.S. Geological Survey recently released provide a hint of the possible contents of a draft Environmental Impact Report being prepared by the state Department of Fish and Game.
That’s the report mandated by the state when then-Gov. Schwarzenegger signed a bill in August 2009 temporarily banning miners from using gasoline-powered dredges to glean flecks of gold from river bottoms. The environmental review was requested to determine how much the popular form of small-scale mining harms salmon.
Former Sen. Sam Aanestad, R-Grass Valley, had opposed the bill, saying it harms businesses in the district: Gold miners spend money on mining equipment, four-wheel drive quads, motorcycles, camping gear and supplies such as food and gasoline.
Statewide, 3,500 dredge permits were issued annually prior to the ban; about 200 people were estimated to mine the waterways and tributaries of Greenhorn Creek and the Yuba, Bear and American rivers.
In 2005, the Karuk tribe sued Fish and Game for allowing the practice of suction dredge mining to occur in areas known to be critical habitat for endangered and at-risk species such as Coho salmon, Pacific lamprey and green sturgeon. The suit ended in a court order in 2006 directing Fish and Game to conduct a CEQA environmental impacts review and amend its regulations. The bill that was signed into law in 2009 invalidated all dredge permits until Fish and Game completes the mandated EIR.
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Vacuum hoses used to suck up heavy metals from the bottom of rivers have the potential to release harmful mercury left behind in the silt from early day miners, dredging opponents say. Suction dredge miners say their practices actually benefit the river and improve habitat for the fish and other organisms that live in it by removing harmful mercury.
Fish and Game was scheduled to begin hosting public meetings during the review period for the draft suction dredge regulations and the draft EIR – in fact, they were set to begin Wednesday and run through Feb. 3 – but those meetings have been postponed for at least two weeks, said Environmental Program Manager Mark Stopher.
“We just got final approval to finalize the document and release the draft EIR and regulations to the public,” Stopher said Wednesday afternoon. “There’s nothing left for us to do except get the documents organized and to the printer.”
Stopher said he expects public review of the documents to begin in mid-February, with the public meetings to start in mid-March.
“Our charge is to determine whether section dredging will be deleterious to the fish, and if it is, we have to write regulations that would allow dredging that wouldn’t be deleterious – that’s our basic authority,” Stopher said.
Stopher would not disclose the contents of the draft EIR report – but he said the report does use information from the two new USGS studies to evaluate the consequences of the effects of suction dredging.
USGS released the results of the studies this week, which examined the potential effects of in-stream suction dredging on mercury contamination in the South Yuba River near its confluence with Humbug Creek.
The studies were requested by the Bureau of Land Management and the California State Water Resources Control Board, to help them assess whether dredging could be used in remediation efforts. The scientists used a 3-inch diameter dredge, consistent with the type commonly used in recreational gold dredging. They scrapped plans to study the effects of an 8-inch diameter dredge after the Regional Water Quality Control Board objected on the grounds that it might damage the environment and wasn’t considered a viable remediation tool, USGS research scientist Charles Alpers said.
According to the study, the site was chosen because it had been a popular site for in-stream dredging for decades and is located just downstream of Malakoff Diggins, one of the state’s largest historical hydraulic gold-mining operations in the late 1800s.
“I think most people recognize suction dredging can do an pretty effective job of removing coarse sediment, but there hasn’t been much study of the finer-grained materials,” Alpers explained. “One of the concerns is what happens to that material during the dredging process.”
The studies on the South Yuba River were undertaken to determine whether the impacts of suction dredge mining are significant or not, Alpers said; he emphasized the USGS is not a regulatory agency.
The studies found that gold dredging that disturbs fine-grained, mercury-laden sediment can allow higher amounts of mercury to enter the environment, potentially threatening food webs far downstream.
Higher concentrations of mercury were found in fine-grained sediment than in coarse-grained sediment in the river and in the nearby streambanks – and because fine grained sediment is more likely to be carried downstream, disturbance of these kinds of sediment likely increases the concentration and amount of mercury downstream, the studies said.
The researchers found elevated concentrations of methylmercury, a toxic form of mercury easily taken up in the food web, in invertebrates collected from the study area. They also found that the fine-grained, mercury-laden sediment from the South Yuba River-Humbug Creek area could produce toxic methylmercury when even very small amounts were mixed with organic-rich sediment from downstream areas such as Englebright Lake and the Sacramento-San Joaquin River Delta.
During the study, the scientists found that present-day suction dredging could be problematic if used as a management tool to remove mercury from the environment.
Although a typical suction dredge might be effective in capturing larger sand-sized particles of mercury and gold-mercury amalgam, Alpers said it is ineffective in capturing finer-grained sediment particles that carry the most mercury. Instead, these smaller particles and the mercury in them, if mobilized by dredging, stay suspended in the water for days and may be carried great distances downstream, increasing the possibility of methylmercury entering the food web.
Methylmercury is a potent neurotoxin that impairs the nervous system, and is especially risky to young children and fetuses. Several water bodies in the Sierra Nevada and elsewhere in California are considered to have impaired water quality and elevated mercury levels in sport fish.
To contact Staff Writer Liz Kellar, e-mail email@example.com or call 477-4229.
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