Suction Dredging for Gold

Does this river look polluted? The environmental groups would have you believe so. This river, located in the Sierra Nevadas of California has been continuously mined for over forty years using a suction dredge. Where’s the garbage and the toxic waste the environmental groups claim miners contribute? It’s not there because miners pick it up and pack it out.

What does the science say? The actual research says the trout in California’s mountain rivers are cleaner than virtually any other fish in the country. A mercury study conducted in 2007 by the California Water Resources Board found that virtually no trout samples collected exceeded the health screening criteria. [Read the full report here]. Multiple studies have found similar results. The single reservoir in the gold mining area near Laporte that had a sample exceeding the threshold was in Sly Creek Reservoir – a reservoir that has no mining activity on any feeder streams and is not in a historical drainage for hydraulic pits – yet the trout had higher mercury levels than trout samples taken from reservoirs that were fed from mining watersheds.

The science and the facts do not support the environmentalist or government claims that dredging releases mercury. The California Regional Water Quality Control Board of dredging and mercury conducted in 2005 using a 4″ standard suction dredge found the dredge removed 98% of the mercury from the watershed [Read the full report here]. A study conducted by the US Geological Survey in 2009 found similar results when using an actual dredge. In fact the 2009 study found that the amount of mercury emitting from the dredge was below threshold detection levels which are measured in parts per trillion. [Read the full report here]

The mercury data in the Subsequent Environmental Impact Report is wrong. The numbers were collected by using a container to collect only the mercury from the bedrock with a closed tank system that recycled the contaminated water back onto the bedrock and pushed the elemental mercury through the pump impeller thousands of time ensuring the mercury would be in almost microscopic form which would cause it to suspend and attach to particles of sediment. The experiment was flawed in design, set up and execution and reflects only the government’s zeal to shut down dredging despite the lack of evidence. It appears the entire purpose of the experiment was to skew the results to build the case against dredging.

All we ask is the science and data reflect the actual impact, but clearly this is too much to ask. The facts have been twisted to achieve a predetermined end. The facts include not a single documented instance of a dredge harming any fish anywhere. The idea that dredges release mercury that would otherwise be trapped is the result of people not understanding either mercury or rivers. Mercury, unlike gold is liquid. Mercury is displaced even during low flow events by gravity. Gold is not. That mercury and gold are found together is because they are dense, but mercury is always moving due to gravity. This fact was confirmed in the 2005 Humphry’s study on dredging and mercury.

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