My Turn: Is lake disposal better for environment?

A Lower Slate Lake dam would be subject to catastrophic failure

Posted: Tuesday, August 14, 2007

This letter is written to address a single issue regarding the Kensington Mine. That question is whether it is environmentally preferable to construct a dam to enlarge Lower Slate Lake and then deposit mine tailings behind that dam, or to use a dry-stack facility.

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I am ignoring the question of whether lake storage of untreated mine waste is legal (it is not), whether the tailings are as benign as the company claims (studies were inconclusive on this point), and pretty much every other issue regarding Kensington.

I believe this narrow question is important because Kensington executives and a number of politicians have continued to repeat the assertion that the use of Lower Slate Lake as a disposal site for mine waste is indeed better for the environment. A few weeks ago one Kensington executive told the Juneau Assembly that the primary reason Coeur Alaska switched from dry stack to lake disposal was for environmental reasons, and the fact that it was less expensive was only a secondary consideration.

The argument for lake disposal hinges on the fact it will use existing wetlands, in other words the lake and its surrounding lake-edge wetlands habitat, and increase the size of both after the dam is constructed. On the other hand, a dry-stack tailings facility, such as the 1997 approved site, would have taken forested wetlands, put the dry-stack facility on top of them, resulting in a large net loss of wetlands.

If you accept this argument, then you must also accept the company's claim that the enlarged lake with 4 million to 10 million tons of mine waste covering its bottom and a few inches of clean fill on top of that, will be successfully re-stocked with Dolly Varden and all the benthic organisms that provide food for them. Even though lake restoration is an unproved assumption, let's also accept that the lake will be at least as productive post mine as it was prior to waste disposal for the sake of argument.

The one thing that the mine company cannot get around is that the dam, located at the head of an enlarged Lower Slate Lake, is subject to catastrophic failure. It will be located next to a major earthquake fault line that runs up the west side of Admiralty Island and then north past the Kensington Mine. The dam will be perched above Berners Bay at the head of a naturally draining watershed that spills steeply down into Slate Creek Cove and Berners Bay.

Consider for a moment the force carried in a lake's worth of moving water. Think of having an entire watershed scoured out by a mixture of lake water and mine tailings, of having a tidal wave of dirt, trees and boulders slamming into Slate Creek Cove with its dock, perhaps occupied by boat and barge, and its adjacent fuel storage facilities, and then washing into Berners Bay.

Never happen you say? Well, never is a long time.

In contrast a dry-stack tailings facility can be located in an area that is not naturally draining and does not have streams coursing through it. The 1997 site, which had the potential to store up to 20 million tons of tailings, is such an area. There also are other sites on the Berners Bay side of the project area that could be looked at for their storage suitability. A dry stack located properly may be subject to being compromised by an earthquake, but even so, the material will not go far. A dry stack can be reconstructed, whereas all the king's men can't put a washed out watershed or Slate Creek Cove back together again.

One more point. The mining company asserts that all of the permitting agencies have agreed that the lake storage option is preferable environmentally. This is not quite the case. The Environmental Protection Agency specifically went on record as saying the 1997 dry-stack plan is the environmentally preferable alternative, and the agency has never changed that assessment.

• Mark Rorick is chairman of the Juneau Group of the Sierra Club and is a Juneau resident.



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