Suction Dredge Mining

NFARA DEIR Comments | FAC DEIR Comments | 5/11 KVMR Interview
County Ag Commission Letter to Supervisors | County Supervisors' Letter

Background information on proposed state regulations governing suction dredge mining, from Jim Ricker's article for the Summer 2011 Community, will be posted shortly. Here are comments submitted to the California Fish and Game Department by NFARA, by FAC, the Foothills Angler Coalition, by the Placer County Board of Supervisors, and by the Placer County Agricultural Commission.

These questions were asked following my KVMR interview on Saturday, May 7, 2011, via email. Bill Carnazzo, Foothills Angler Coalition Vice President and avid angler, has answered them. Please let me know if the following findings have been disproved or you have additional information.

Bill Carnazzo's responses are based on information from the studies cited in the draft SEIR published by DFG, along with its proposed regulations, and on personal knowledge accumulated over many years of on-the-river observation:

1. Question: Most miners with valid claims are stewards of the rivers they work, protecting their interests as well. Their regulated suction practices remove the mercury along with the gold, and the mercury is not returned to the river, but stored and disposed of properly by the miners.
   Answer: It is generally (although not universally) true that some elemental Hg is pulled from the substrate by dredges, and removed via the sluice that receives the pump effluent. The SEIR contains some statistics on how much is actually removed--which is very little. It is not clear how many miners observe proper disposal practices because it involves effort and expense. The main issue with Hg resuspension via the dredging process is not elemental Hg; rather, it is the "methylization" of Hg when it is exposed, in small-particle form, to UV light and Oxygen. Methylized Hg is highly toxic, in that it is absorbed into virtually every cell in aquatic organisms. It has been shown scientifically that it causes birth defects in humans, and is carcinogenic. Thus, the marginal benefit of removal of minor amounts of elemental Hg is far outweighed by the damage to aquatic life, and ultimately to human life, caused by methylized Hg.


2. Question: An end result of the practice of regulated suction dredging actually enhances the quality of the gravel beds necessary during spawning season. On dammed rivers, the natural spring high water "first flush" that natures uses for that purpose is sometimes impeded during low water years effecting the results of the spawn.
   Answer: All of the science used in the DFG analyses of the effects of dredging on spawning habitat for trout and anadromous fish reaches the conclusion that the effects are deleterious and in some cases permanent. Dredging, in order to be successful in terms of gold production, requires that the dredger get down to bedrock where the gold is located (along with the other heavy metal, elemental Hg). Spawning gravels are completely removed from the substrate, and large rocks (which have a protective effect on the substrate) are displaced and moved to the side of the river. While some of the displaced substrate does wash downstream, and some is replenished in the winter and spring when the natural hydrograph (in most years) results in pulse flows, the recovery cycle for substrate differs from that of spawning fish. In other words, there is a cyclic disconnect between substrate recovery and fish spawning. In turn, this produces a downward spiral in fish production. In short, the substrate disturbance by dredgers creats an unnatural adverse effect on the river, which disturbs spawning activity.


3. Question: Sediment flush happens every spring regardless of human intervention. It is just nature's way.
   Answer: It is, in a very general way, true that the spring hydrograph results in initiation of silt and gravel motion in some cases; the same can be said of the silts that are introduced into the water column by dredging, and deposited elsewhere. What is clear, however, is that dredging reintroduces silt to the water column and upper levels of substrate, when it would otherwise have remained buried. In turn, this silt contains small particles of Hg, which is easily methylized, with the adverse effects of that process as mentioned above.

In summary, the mining community is prone to making general, mostly unsupported claims and trotting out handy one-liners that oversimplify a hugely complicated set of issues. The truth is that all of the credible science supports the conclusion that all of the effects of dredging on rivers are adverse and significant to the individual river being dredged.

Updated 5/16/11